* screen sharing for desktop (WIP).
* use git repo for testing.
* update.
* Add sourceId/frameRate to ScreenShareCaptureOptions.
* Compatible with flutter web.
* Rendering of camera and screenshare video tracks at same time.
* Remote screen sharing is shown first, and fixed sub/unsub button for screenshare widget.
* resolved conflict.
* modify flutter-webrtc to pub version.
* remove unused import.
* chore: Common params for Camera and ScreenShare.
