3516 [shared_preferences_windows]-Migrate to null safety (cla: yes, nnbd, p: shared_preferences, platform-windows)

3518 [camera_platform_interface] Added stopRecordingVideo (cla: yes, p: camera)

3521 Add section about how to use Material components in an app using WebView (cla: yes, p: webview_flutter)

3522 [url_launcher_web] Migrate to null-safety (cla: yes, nnbd, p: url_launcher, platform-web)

3523 [shared_preferences] Migrate platform plugins to null-safety (cla: yes, nnbd, p: shared_preferences, platform-linux, platform-web)

3524 [image_picker] Migrate to null-safety (cla: yes, nnbd, p: image_picker)