MediaController: Make getTag() public

This removes hidden API usages from the framework to the apex, which
would be prohibited.

Test: Build
Bug: 123485698
Change-Id: Ib3c350bad4af2e8db3788296dc78b7f7eb0693c0

api/current.txt

@@ -27355,6 +27355,7 @@ package android.media.session {
     method public int getRatingType();
     method @Nullable public android.app.PendingIntent getSessionActivity();
     method @NonNull public android.media.session.MediaSession.Token getSessionToken();
+    method public String getTag();
     method @NonNull public android.media.session.MediaController.TransportControls getTransportControls();
     method public void registerCallback(@NonNull android.media.session.MediaController.Callback);
     method public void registerCallback(@NonNull android.media.session.MediaController.Callback, @Nullable android.os.Handler);

media/apex/java/android/media/session/MediaController.java

@@ -485,7 +485,6 @@ public final class MediaController {
      * Get the session's tag for debugging purposes.
      *
      * @return The session's tag.
-     * @hide
      */
     public String getTag() {
         if (mTag == null) {