4504 [path_provider] Fix links in READMEs (cla: yes, waiting for tree to go green, p: path_provider, platform-ios, platform-android, platform-macos, platform-linux)

4505 [shared_preferences] Federate mobile implementations (cla: yes, p: shared_preferences, platform-ios, platform-android)

4506 Enable camera/quick_actions tests  (cla: yes, waiting for tree to go green)

4507 [url_launcher] Add null check for extracting browser headers (cla: yes, waiting for tree to go green, p: url_launcher, platform-android)

4508 [battery] Recreate Android example (cla: yes, p: battery, platform-android, needs tests)

4509 [webview_flutter] Add onUrlChanged callback to platform interface. (cla: yes, waiting for tree to go green, p: webview_flutter)