8550 Export extern constants in embedder.h (cla: yes)

8551 Android Embedding PR30: Make FlutterView focusable so that the keyboard can interact with it. (cla: yes)

8555 Roll Dart 15b11b018364ce03…a8f3a5dae6203d10 (cla: yes)

8557 Update README.md (cla: yes)

8562 Add missing  include to text_input_model.h (cla: yes)

8563 Remove unused import in FlutterActivityDelegate (cla: yes)

8565 Make Rect and RRect use 64 bit doubles, and make them const-able (cla: yes)

8581 Remove the flutter_aot GN argument. (cla: yes)