3588 [connectivity_macos] move NNBD to stable (cla: yes, nnbd, p: connectivity, platform-macos, waiting for tree to go green)

3589 [sensors] Update to NNBD stable (cla: yes, nnbd, p: sensors)

3590 [google_maps_flutter] fixed a small bug in example app. (cla: yes, p: google_maps_flutter)

3591 [camera] Fix iOS rotation issue (cla: yes, p: camera, platform-ios, waiting for tree to go green)

3592 [camera] Fix example from README.md (cla: yes, p: camera, waiting for tree to go green)

3593 [cross_file] Stable null safety release (cla: yes, nnbd, p: cross_file)