Output switcher header is not updated with the latest media content

-Register media controller callback
-Update panel header when medadata changes
-Add test cases

Bug: 151396986
Test: make -j50 RunSettingsRoboTests
Change-Id: Id0b8f997899a96c0c94ca6bf099e624a9e87795b

src/com/android/settings/panel/MediaOutputGroupPanel.java

@@ -148,7 +148,7 @@ public class MediaOutputGroupPanel implements PanelContent, LocalMediaManager.De
     @Override
     public void onDeviceListUpdate(List<MediaDevice> devices) {
         if (mCallback != null) {
-            mCallback.onGroupChanged();
+            mCallback.onHeaderChanged();
         }
     }