2272 [sensors] Documentation and test improvements (cla: yes)

2273 [video_player] Add platform interface (cla: yes)

2274 [url_launcher] DartDoc and test improvements (cla: yes)

2275 Update cirrus to create IOS simulator on 13.2 an xCode 11 (cla: yes)

2280 Add google_sign_in_web plugin. (cla: yes)

2281 [connectivity] Fix reachability stream for iOS (cla: yes)

2282 Migrate plugins to use e2e tests. (cla: yes)

2284 [path_provider] Add v2 embedding support for (cla: yes)

2286 [video_player] Improve DartDocs and test coverage (cla: yes)