12706 Check for a null input method subtype

12708 Cleanup: Turned on NS_ASSUME_NONNULL_BEGIN for FlutterViewController.

12710 Set transparent background in textarea elements

12725 Expanded channel buffer resize to method channels.

12728 Remove unused import in the scenario app

12730 Stop setting the accessibility text if a node has SCOPES_ROUTE set.

12733 [flutter_runner] Make rd and rx uniform

12746 Send AccessibilityEvent.TYPE_VIEW_FOCUSED when input focus is set.

12754 Fix Metal builds by accounting for the updated SubmitFrame signature.

12775 Added some thread asserts to the code and made ios_surface_ safe since