Allow importing RCTAppDelegate in Swift

[okwasniewski]

Summary:

This PR fixes importing RCTAppDelegate, cleans up the imports, and properly sets the background color for bridgeless mode when using RCTRootViewFactory.

The issue with importing to Swift was that RCTTurboModuleManager has C++ in headers which caused Swift to error out.

Changelog:

[IOS] [FIXED] - Allow importing RCTAppDelegate in Swift
[INTERNAL] [REMOVED] - Remove unnecessary imports in AppDelegate
[INTERNAL] [FIXED] - Properly set background color for bridgeless

Test Plan:

• CI Green
• Check if background color is correct

[facebook-github-bot]

@cipolleschi has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	18,008,347	-16
android	hermes	armeabi-v7a	n/a	--
android	hermes	x86	n/a	--
android	hermes	x86_64	n/a	--
android	jsc	arm64-v8a	21,366,891	+8
android	jsc	armeabi-v7a	n/a	--
android	jsc	x86	n/a	--
android	jsc	x86_64	n/a	--

Base commit: 1c69100
Branch: main

[facebook-github-bot]

@cipolleschi merged this pull request in 7c95369.