25395 Deduplicate plugin registration logic and make error logs visible - take 2 (platform-android, cla: yes, waiting for tree to go green)

25453 Add automatic onBackPressed behavior to FlutterFragment (platform-android, cla: yes)

25544 Reduce the warning severity for FlutterEngineGroup (platform-android, cla: yes, waiting for tree to go green)

25575 change the Android FlutterEngine class doc around multiple engines (platform-android, cla: yes, waiting for tree to go green)

25578 Add more doc for how the plugin registration process works and how to customize it (platform-android, cla: yes, waiting for tree to go green)

25619 [flutter_releases] Flutter Stable 2.0.5 Engine Cherrypicks (platform-android, cla: yes, platform-web, platform-windows, platform-fuchsia)