2297 [share] README update

Plugin: Shared Preferences

General bug fixes in the Shared Preferences plugin.

2241 [Shared_preferences]suppress warnings

2296 [shared_preferences] Add missing DartDoc

Plugin: Url launcher

We upgraded the Url launcher plugin to the new plugin API,
and fixed some bugs. Meanwhile,
we have converted the Url launcher into a federated plugin
to help it scale more efficiently to multiple platforms.
For more information, refer to Federated plugins.

2038 [url_launcher] Removed reference to rootViewController during initialization

2136 [url_launcher_web] Fix README.md pubspec example

2217 [url_launcher] Add url_launcher_platform_interface package