Scene support for alerts

[HeyImChris]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native-macos 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native-macos 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Summary

We hit a bug downstream with the existing implementation where we use Scenes in our app which require alerts to be presented from a window associated with the app's UIWindowScene.

Currently without this fix, when we attempt to create a new UIWindow and UIViewController to present a modal alert, that UIWindow isn't associated with any of the app's scenes which results in the app silently failing to show the alert.

The fix is to more or less revert the incriminating part of this change. This is the least intrusive way to make a safe fix, but once this is in, I'd like to make a fuller fix where we find a reasonable way to pair the new UIWindow with the app's scene and continue using that instead.

Changelog

[iOS] [Alert] - Fix modal alert issue using UIScenes

Test Plan

Tested in a downstream app and this is required to show an alert in response to an action sheet closing in an app leveraging UIScenes.

[pull-bot]

	Warnings
⚠️	❔ Base Branch - The base branch for this PR is something other than master. Are you sure you want to merge these changes into a stable release? If you are interested in backporting updates to an older release, the suggested approach is to land those changes on master first and then cherry-pick the commits into the branch for that release. The Releases Guide has more information.

Messages

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