3662 [google_maps_flutter_web] update min flutter sdk version to 1.20.0 (cla: yes, p: google_maps_flutter, platform-web, waiting for tree to go green)

3673 [google_maps_flutter_web] Make google_maps_flutter_web work with latest plugins  (cla: yes, p: google_maps_flutter, platform-web)

3675 [google_maps_flutter_web] Move integration tests to example. (cla: yes, p: google_maps_flutter, platform-web)

3679 [google_maps_flutter_web] Downgrade mockito in example app. (cla: yes, p: google_maps_flutter, platform-web)

3694 [extension_google_sign_in_as_googleapis_auth] Deleted. (cla: yes, p: google_sign_in, platform-android, platform-ios, platform-web)