Automatic update of RCT-Folly (#32659)

Summary:
When upgrading `react-native`, the version `RCT-Folly` defined [here](https://github.com/facebook/react-native/blob/main/third-party-podspecs/RCT-Folly.podspec) can change. If that happens, if you run `pod install` after `yarn install`, you will get a similar error to this:
```
[!] CocoaPods could not find compatible versions for pod "RCT-Folly":
  In snapshot (Podfile.lock):
    RCT-Folly (from `../node_modules/react-native/third-party-podspecs/RCT-Folly.podspec`)

  In Podfile:
    RCT-Folly (from `../node_modules/react-native/third-party-podspecs/RCT-Folly.podspec`)

    React-RCTNetwork (from `../node_modules/react-native/Libraries/Network`) was resolved to 0.66.3, which depends on
      RCT-Folly (= 2021.06.28.00-v2)
```

This error occurs because `Cocoapods` does not update pods that point to a local podspec. Locally, you could resolve this issue by running `pod update RCT-Folly --no-repo-update`. On the CI, you have to do a clean checkout (in case you cache the `Pods` folder which we do). All of this makes upgrading `react-native` painful - for the whole community and for us shopify

There are other users who have struggled with this, such as [here](#32423). The suggestion there is to delete `Podfile.lock` which is unnecessary - but it shows that users are confused what to do with this error and is something worth fixing.

To mitigate these issues, `react_native_pods.rb` automatically marks `RCT-Folly` as changed in the [detect_changes_with_podfile method](https://github.com/CocoaPods/Core/blob/master/lib/cocoapods-core/lockfile.rb#L289) from `Pod::Lockfile` if the version in `node_modules/react-native/third-party-podspecs/RCT-Folly.podspec` and `Pods/Local Podspecs/RCT-Folly.podspec.json` mismatch.

Instead of automatically updating the local podspec (in `Pods/Local Podspecs` directory) we could also:
a) integrate `RCT-Folly` as a local pod (such as `React-Core` and others)
b) integrate `RCT-Folly` as an external dependency (going through Cocoapods' centralized repository)

I don't have enough context on why `RCT-Folly` is bundled the way it is, so I am open to suggestions here.

## Changelog

<!-- Help reviewers and the release process by writing your own changelog entry. For an example, see:
https://github.com/facebook/react-native/wiki/Changelog
-->

[iOS] [Fixed] - Fix `pod install` when `RCT-Folly` version has been updated.

Pull Request resolved: #32659

Test Plan:
I have created a [repository](https://github.com/fortmarek/react-native-upgrade-reproduction) where you can reproduce the issue. You can simply:
1) clone the repo (`git clone https://github.com/fortmarek/react-native-upgrade-reproduction`)
2) Run `yarn install && cd ios && pod install`
3) Change `react-native` version in `package.json` to `0.66.3`
4) Run again `yarn install && pod install`
5) Observe error

To test the fix, you can then:
1) copy-paste the `react_native_pods.rb` file from this branch to `react-native-upgrade-reproduction/node_modules/scripts/react_native_pods.rb`
2) run `pod install` again

This time, the `pod install` command should succeed.

Reviewed By: sota000

Differential Revision: D32720758

Pulled By: cortinico

fbshipit-source-id: 940db9c9f0530f896e47b676dec46bc93cea0085

scripts/react_native_pods.rb

@@ -119,6 +119,15 @@ def use_react_native! (options={})
     end
     pod 'libevent', '~> 2.1.12'
   end
+
+  pods_to_update = LocalPodspecPatch.pods_to_update(options)
+  if !pods_to_update.empty?
+    if Pod::Lockfile.public_instance_methods.include?(:detect_changes_with_podfile)
+      Pod::Lockfile.prepend(LocalPodspecPatch)
+    else
+      Pod::UI.warn "Automatically updating #{pods_to_update.join(", ")} has failed, please run `pod update #{pods_to_update.join(" ")} --no-repo-update` manually to fix the issue."
+    end
+  end
 end
 
 def get_default_flags()
@@ -696,3 +705,46 @@ def __apply_Xcode_12_5_M1_post_install_workaround(installer)
   time_header = "#{Pod::Config.instance.installation_root.to_s}/Pods/RCT-Folly/folly/portability/Time.h"
   `sed -i -e  $'s/ && (__IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_10_0)//' #{time_header}`
 end
+
+# Monkeypatch of `Pod::Lockfile` to ensure automatic update of dependencies integrated with a local podspec when their version changed.
+# This is necessary because local podspec dependencies must be otherwise manually updated.
+module LocalPodspecPatch
+  # Returns local podspecs whose versions differ from the one in the `react-native` package.
+  def self.pods_to_update(react_native_options)
+    prefix = react_native_options[:path] ||= "../node_modules/react-native"
+    @@local_podspecs = Dir.glob("#{prefix}/third-party-podspecs/*").map { |file| File.basename(file, ".podspec") }
+    @@local_podspecs = @@local_podspecs.select do |podspec_name|
+      # Read local podspec to determine the cached version
+      local_podspec_path = File.join(
+        Dir.pwd, "Pods/Local Podspecs/#{podspec_name}.podspec.json"
+      )
+
+      # Local podspec cannot be outdated if it does not exist, yet
+      next unless File.file?(local_podspec_path)
+
+      local_podspec = File.read(local_podspec_path)
+      local_podspec_json = JSON.parse(local_podspec)
+      local_version = local_podspec_json["version"]
+
+      # Read the version from a podspec from the `react-native` package
+      podspec_path = "#{prefix}/third-party-podspecs/#{podspec_name}.podspec"
+      current_podspec = Pod::Specification.from_file(podspec_path)
+
+      current_version = current_podspec.version.to_s
+      current_version != local_version
+    end
+    @@local_podspecs
+  end
+
+  # Patched `detect_changes_with_podfile` method
+  def detect_changes_with_podfile(podfile)
+    changes = super(podfile)
+    @@local_podspecs.each do |local_podspec|
+      next unless changes[:unchanged].include?(local_podspec)
+
+      changes[:unchanged].delete(local_podspec)
+      changes[:changed] << local_podspec
+    end
+    changes
+  end
+end