Fix: Visibility Optimization randomly not working (#65)

* use widget id instead of state id

* ignore local video view events

* switch remote view visibility also

* use Key for a reliable id

* remove local check

* clean up

* redesign

* check mounted

* remove mount check

* more optimization

* quick wake up

* mark internal

* rename to adaptiveStream

example/lib/widgets/participant.dart

@@ -174,7 +174,7 @@ class _RemoteParticipantWidgetState
     for (final trackPublication in widget.participant.videoTracks) {
       print(
           'video track ${trackPublication.sid} subscribed ${trackPublication.subscribed} muted ${trackPublication.muted}');
-      if (trackPublication.subscribed && !trackPublication.muted) {
+      if (trackPublication.subscribed && !trackPublication.muted && _visible) {
         return trackPublication.track;
       }
     }