11844 Updated API usage in scenario app by deleting unnecessary method.

11902 Remove un-needed FragmentActivity import statements to facilitate proguard.

12305 Introduce flutterfragmentactivity

12328 Added javadoc comments to FlutterActivity and FlutterFragmentActivity.

12359 Forwards Flutter View to platform views and detaches when needed.

12362 Fixes race condition that was reported internally.

12806 Move initialization into FlutterEngine

12987 Added FlutterActivity and FlutterFragment hook to cleanUpFlutterEngine() as symmetry for configureFlutterEngine(). (#41943)

13214 Forwards Activity result to FlutterFragment in FlutterFragmentActivity.

13215 Adds Dark Mode support to new Android embedding (this was accidentally missed previously).