4172 [flutter_plugin_tools] Make firebase-test-lab fail when no tests run (cla: yes)

4175 [camera_web] Add availableCameras implementation (cla: yes, waiting for tree to go green, p: camera, platform-web)

4176 [flutter_plugin_tools] Replace xctest and java-test with native-test (cla: yes)

4178 [webview_flutter] Refactored creation of Android WebView for testability. (cla: yes, waiting for tree to go green, p: webview_flutter, platform-android)

4181 [image_picker] Move UI test (cla: yes, waiting for tree to go green, p: image_picker, platform-ios)

4182 [camera_web] Add createCamera implementation (cla: yes, waiting for tree to go green, p: camera, platform-web)