Mark broadcast receivers as not exported

They are called from the system only and don't need to be exported
to be visible to other apps.

PiperOrigin-RevId: 489210264

libraries/session/src/main/java/androidx/media3/session/MediaSessionImpl.java

@@ -216,8 +216,7 @@ import org.checkerframework.checker.initialization.qual.Initialized;
       broadcastReceiver = new MediaButtonReceiver();
       IntentFilter filter = new IntentFilter(Intent.ACTION_MEDIA_BUTTON);
       filter.addDataScheme(castNonNull(sessionUri.getScheme()));
-      // TODO(b/197817693): Explicitly indicate whether the receiver should be exported.
-      context.registerReceiver(broadcastReceiver, filter);
+      Util.registerReceiverNotExported(context, broadcastReceiver, filter);
     } else {
       // Has MediaSessionService to revive playback after it's dead.
       Intent intent = new Intent(Intent.ACTION_MEDIA_BUTTON, sessionUri);

libraries/ui/src/main/java/androidx/media3/ui/PlayerNotificationManager.java

@@ -1164,8 +1164,7 @@ public class PlayerNotificationManager {
     Notification notification = builder.build();
     notificationManager.notify(notificationId, notification);
     if (!isNotificationStarted) {
-      // TODO(b/197817693): Explicitly indicate whether the receiver should be exported.
-      context.registerReceiver(notificationBroadcastReceiver, intentFilter);
+      Util.registerReceiverNotExported(context, notificationBroadcastReceiver, intentFilter);
     }
     if (notificationListener != null) {
       // Always pass true for ongoing with the first notification to tell a service to go into