3493 Add plugin issue query to README (cla: yes, waiting for tree to go green)

3494 [in_app_purchases] Remove TypeMatcher reference (cla: yes, p: in_app_purchase)

3495 Remove cyanglaz from CODEOWNER: google_sign_in, connectivity, package_info, video_player (cla: yes, waiting for tree to go green)

3496 [camera] Revert compileSdkVersion back to 29 (cla: yes, p: camera, platform-android, waiting for tree to go green)

3497 [camera_platform_interface] Migrate to null safety (cla: yes, nnbd, p: camera)

3498 [path_provider] Update macOS for NNBD (cla: yes, nnbd, p: path_provider, platform-macos)