3930 [sensors] Update Cirrus image to Xcode 12.5, fix sensors analyzer warning  (cla: yes, p: sensors, platform-ios)

3932 Move integration test to null safety for multiple plugins (cla: yes, p: webview_flutter, p: image_picker, p: in_app_purchase, p: wifi_info_flutter, p: quick_actions, p: connectivity, p: device_info, platform-ios, platform-android, platform-macos)

3934 Enable NNBD for more plugin integration tests (cla: yes, p: camera, p: google_maps_flutter, p: local_auth, p: url_launcher, p: shared_preferences, platform-windows, platform-macos, platform-linux)

3936 Added Windows to the description (cla: yes, waiting for tree to go green, p: path_provider)