3442 Windows nullsafety prep (cla: yes)

3444 [camera] Ensure that channel.invokeMethod runs on the main thread (cla: yes, p: camera, waiting for tree to go green)

3449 [google_maps_flutter_platform_interface] Fixes for custom tiles (cla: yes, p: google_maps_flutter, waiting for tree to go green)

3459 Revert “[ci][image_picker]enable xcode 12/iOS 14 for all tasks except lint” (cla: yes, p: image_picker)

3462 Support breaking http change (cla: yes, p: cross_file)

3463 bump vmservice (cla: yes, p: integration_test)

3465 [path_provider] drop uuid (cla: yes, p: path_provider)