4248 [flutter_plugin_tools] Fix build-examples for packages (cla: yes)

4249 [webview] Fix typos in the README (cla: yes, waiting for tree to go green, p: webview_flutter, last mile)

4250 Fix crash from null Google Maps object (cla: yes, waiting for tree to go green, p: google_maps_flutter, platform-android)

4251 [google_sign_in] adds option to re-authenticate on google silent sign in (cla: yes, waiting for tree to go green, p: google_sign_in)

4252 [flutter_plugin_tools] Introduce a class for packages (cla: yes)

4254 [flutter_plugin_tools] Improve process mocking (cla: yes)