1353 [firebase_messaging] Update example (cla: yes, submit queue)

1357 Disable Android emulator testing for now to fix tests (cla: yes)

1360 [webview_flutter] Create WebView client depending on version and hasDelegate (bugfix, cla: yes, webview)

1361 [webview_flutter] Update changelog and bump versions. (cla: yes, submit queue)

1364 [firebase_ml_vision] Update ImageDetector for iOS (bugfix, cla: yes, flutterfire)

1367 [firebase_ml_vision] Android side of upgrade to new ImageLabeler (bugfix, cla: yes, flutterfire)

1369 [webview_flutter] Refactor WebViewController to have a reference to the widget, to minimize necessary update calls. (cla: yes)