9376 libtxt: remove obsolete font_manager_available defines (cla: yes)

9377 A fix for the platform view dismiss crash related to gl (cla: yes)

9378 Wire intent args for observatory port (cla: yes)

9383 Update Metal backend to account for Skia updates. (cla: yes)

9384 Android Embedding Refactor PR34: Fill in missing nullability annotations (cla: yes)

9385 Add Dart SDK > 2.3.0 constraint to license script (cla: yes)

9388 Added unit tests for the ios code. (cla: yes)

9391 Android Embedding Refactor PR35: Ensure all JNI methods are in FlutterJNI. (cla: yes)

9394 Remove build flags for dynamic patching (cla: yes)