3239 Remove unused test dependencies add missing environment constraints (cla: yes)

3243 [google_sign_in] fix deprecated member use (cla: yes)

3245 [video_player] Android: Dispose video players when app is closed (cla: yes)

3249 [Path Provider] Migrate platform interface to nnbd (cla: yes)

3253 [camera] Add camera_platform_interface package (cla: yes)

3254 [image_picker] Set up XCUITests (cla: yes)

3255 [local_auth] Migrate to null safety. (cla: yes)

3258 [camera] Move camera to camera/camera (cla: yes)

3259 [webview_flutter] update documentation to indicate gesture handling issues on iOS 13.4 and 13.5 (cla: yes)