Add optional return_value_from_void_function rule using SwiftSyntax

[marcelofabri]

See #3015

This adds SwiftSyntax as a submodule, which should workaround an issue with SPM + Xcode, while keeping development flow similar.

We could move everything to SPM, but that's more work that I can handle now, so I hope we can move forward with this PR, which will enable using SwiftSyntax to create more complex rules.

This rule is opt-in because it's slower than the other ones.

[SwiftLintBot]

	106 Warnings
⚠️	Big PR
⚠️	This PR introduced a violation in Aerial: /Aerial/Source/Views/PrefPanel/InfoTableSource.swift:125:44: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Alamofire: /Source/MultipartFormData.swift:433:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Alamofire: /Source/MultipartFormData.swift:438:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Alamofire: /Source/MultipartFormData.swift:469:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Alamofire: /Source/MultipartFormData.swift:479:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Alamofire: /Source/Protector.swift:66:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /UITests/EarlGrey.swift:118:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /UITests/EarlGrey.swift:126:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /ClientTests/FxAPushMessageTest.swift:34:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Shared/DeferredUtils.swift:26:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Shared/DeferredUtils.swift:45:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Extensions/NotificationService/NotificationService.swift:24:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Extensions/NotificationService/NotificationService.swift:94:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Extensions/ShareTo/SendToDevice.swift:32:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:17:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:21:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:25:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:109:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:115:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:119:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:225:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:235:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:242:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /PushTests/PushCryptoTests.swift:250:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Frontend/Library/LibraryViewController/LibraryViewController+LibraryPanelDelegate.swift:39:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Frontend/Login Management/LoginListViewController.swift:613:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Frontend/Browser/FocusHelper.swift:28:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Frontend/Browser/FocusHelper.swift:33:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Frontend/Browser/FocusHelper.swift:42:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Frontend/Browser/Tab.swift:566:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Frontend/Browser/TabManager.swift:722:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Frontend/Widgets/PhotonActionSheet/PhotonActionSheet.swift:289:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Frontend/Browser/BrowserViewController.swift:1630:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:93:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:130:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:137:17: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:150:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:162:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:172:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:183:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:209:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:213:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Helpers/FxALoginHelper.swift:251:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Application/AppDelegate.swift:639:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Firefox: /Client/Application/AppDelegate.swift:662:17: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Kickstarter: /Library/KeyValueStoreType.swift:130:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Nimble: /Tests/NimbleTests/Helpers/utils.swift:54:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Nimble: /Sources/Nimble/Matchers/Async.swift:107:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Nimble: /Sources/Nimble/Matchers/Async.swift:179:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Nimble: /Sources/Nimble/DSL+Wait.swift:24:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Nimble: /Sources/Nimble/DSL+Wait.swift:34:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Realm: /RealmSwift/LinkingObjects.swift:157:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Realm: /RealmSwift/Sync.swift:431:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Realm: /RealmSwift/Results.swift:191:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Realm: /RealmSwift/List.swift:163:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Realm: /Realm/Tests/Swift/RLMSupport.swift:114:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Realm: /Realm/Swift/RLMSupport.swift:114:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Sourcery: /Pods/Nimble/Sources/Nimble/Matchers/Async.swift:107:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Sourcery: /Pods/Nimble/Sources/Nimble/Matchers/Async.swift:179:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Sourcery: /Pods/Nimble/Sources/Nimble/DSL+Wait.swift:24:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Sourcery: /Pods/Nimble/Sources/Nimble/DSL+Wait.swift:34:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Sourcery: /Sourcery/Sourcery.swift:570:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Sourcery: /SourceryTests/Stub/Performance-Code/Kiosk/HelperFunctions.swift:49:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/SwiftNativeNSArray.swift:99:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/SwiftNativeNSArray.swift:182:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/MigrationSupport.swift:335:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/StringUTF16View.swift:615:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/String.swift:943:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:541:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:634:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:737:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:767:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:835:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:943:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:974:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1013:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1055:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1162:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1193:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1232:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1343:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1429:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1521:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1615:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:1941:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:2151:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ExistentialCollection.swift:2369:7: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/ContiguousArrayBuffer.swift:151:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/KeyPath.swift:65:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/Darwin/AssetsLibrary/ALAssetsLibrary.swift:27:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/Darwin/Foundation/NSString.swift:85:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/public/Darwin/Foundation/AffineTransform.swift:157:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/private/SwiftPrivateLibcExtras/SwiftPrivateLibcExtras.swift:77:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/private/StdlibUnittestFoundationExtras/StdlibUnittestFoundationExtras.swift:95:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/private/StdlibUnittestFoundationExtras/StdlibUnittestFoundationExtras.swift:118:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/private/StdlibUnittest/RaceTest.swift:721:40: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/private/StdlibCollectionUnittest/MinimalCollections.swift:391:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in Swift: /stdlib/private/StdlibCollectionUnittest/MinimalCollections.swift:490:5: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in WordPress: /WordPress/Classes/ViewRelated/Gutenberg/Utils/GutenbergFilesAppMediaSource.swift:48:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in WordPress: /WordPress/Classes/ViewRelated/Gutenberg/Utils/GutenbergFilesAppMediaSource.swift:52:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in WordPress: /WordPress/Classes/ViewRelated/Gutenberg/Utils/GutenbergStockPhotos.swift:49:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in WordPress: /WordPress/Classes/ViewRelated/Gutenberg/GutenbergViewController.swift:86:9: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in WordPress: /WordPress/Classes/Services/EditorSettingsService.swift:12:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in WordPress: /WordPress/Classes/Services/EditorSettingsService.swift:17:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)
⚠️	This PR introduced a violation in WordPress: /WordPress/WordPressTest/BlogServiceDeduplicationTests.swift:128:13: warning: Return Value from Void Function Violation: Returning values from Void functions should be avoided. (return_value_from_void_function)

	12 Messages
📖	Linting Aerial with this PR took 1.27s vs 1.18s on master (7% slower)
📖	Linting Alamofire with this PR took 2.27s vs 2.18s on master (4% slower)
📖	Linting Firefox with this PR took 9.37s vs 8.96s on master (4% slower)
📖	Linting Kickstarter with this PR took 15.38s vs 14.63s on master (5% slower)
📖	Linting Moya with this PR took 1.21s vs 1.17s on master (3% slower)
📖	Linting Nimble with this PR took 1.4s vs 1.34s on master (4% slower)
📖	Linting Quick with this PR took 0.58s vs 0.53s on master (9% slower)
📖	Linting Realm with this PR took 2.41s vs 2.36s on master (2% slower)
📖	Linting SourceKitten with this PR took 1.04s vs 0.99s on master (5% slower)
📖	Linting Sourcery with this PR took 6.83s vs 6.62s on master (3% slower)
📖	Linting Swift with this PR took 12.78s vs 12.25s on master (4% slower)
📖	Linting WordPress with this PR took 15.38s vs 14.9s on master (3% slower)

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