3526 [shared_preferences] Migrate main package to null-safety (cla: yes, p: shared_preferences, platform-android, platform-ios, platform-macos, platform-web)

3527 Add plugin tools as a git submodule and depend on it directly (cla: yes)

3528 [file_selector_web] Fix typo in pubspec. (cla: yes, p: file_selector, platform-web)

3530 [camera_platform_interface] Migrate to null safety (cla: yes, p: camera)

3532 Add post merge labeler (cla: yes)

3533 [camera] NNBD migration of the camera plugin (cla: yes, p: camera, platform-ios)