Changed StoreKit2Setting.default back to `.enabledOnlyForOptimizati…

…ons` (#2022)

This changes the default back to `StoreKit 1`. We decided to do this for
the following reasons:
- Purchasing with `PromotionalOffer`s does not work with StoreKit 2 due
to an Apple bug (see
#2020 (comment))
- `checkTrialOrIntroDiscountEligibility` is significantly slower with
`StoreKit 2` (#1893). We're adding optimizations to help with that
(#2007), but the underlying logic will still be slow.
- A rare race-condition where `StoreKit 2` does not have transactions
after a purchase ([TRIAGE-82]). We have some workarounds (#1945), but
it's still being investigated.

_Note: This effectively reverts 0ee540a. That commit made it easier to
only change the default in one place which is why this PR is basically
just one line._

[TRIAGE-82]:
https://revenuecats.atlassian.net/browse/TRIAGE-82?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Sources/Misc/StoreKit2Setting.swift

@@ -34,7 +34,7 @@ extension StoreKit2Setting {
             : .enabledOnlyForOptimizations
     }
 
-    static let `default`: Self = .enabledForCompatibleDevices
+    static let `default`: Self = .enabledOnlyForOptimizations
 
 }
 

Sources/Purchasing/Configuration.swift

@@ -135,8 +135,8 @@ import Foundation
 
         /**
          * Set `usesStoreKit2IfAvailable`.
-         * - Parameter usesStoreKit2IfAvailable: opt out of using StoreKit 2 on devices that support it.
-         * Defaults to  `true`.
+         * - Parameter usesStoreKit2IfAvailable: opt in using StoreKit 2 on devices that support it.
+         * Defaults to  `false`.
          */
         @objc public func with(usesStoreKit2IfAvailable: Bool) -> Builder {
             self.storeKit2Setting = .init(useStoreKit2IfAvailable: usesStoreKit2IfAvailable)