3934 Enable NNBD for more plugin integration tests (cla: yes, p: camera, p: google_maps_flutter, p: local_auth, p: url_launcher, p: shared_preferences, platform-windows, platform-macos, platform-linux)

3960 Use collection and box literals in ObjC code (cla: yes, p: webview_flutter, p: camera, p: google_maps_flutter, p: image_picker, p: in_app_purchase, platform-ios)

3972 Clean up cruft in pubspec.yaml files (cla: yes, p: battery, p: camera, p: google_maps_flutter, p: google_sign_in, p: image_picker, p: in_app_purchase, p: plugin_platform_interface, p: url_launcher, p: shared_preferences, p: sensors, platform-windows, platform-web)