title: How can I receive action of PlayerNotificationManager notification button like stop?
body: <p>I use Exoplayer and bind with PlayerNotificationManager to handle player action on the notification. It works fabulous but I want to get a listener or receiver when stop button pressed from notification. Right now when I click on the stop button player was stuck.</p>
  
  <pre><code>playerNotificationManager = PlayerNotificationManager.createWithNotificationChannel(
          this,
          "playback_channel",
          R.string.exo_download_notification_channel_name,
          1,
          object : PlayerNotificationManager.MediaDescriptionAdapter {
              override fun createCurrentContentIntent(player: Player?): PendingIntent? {
                  val intent = Intent(context, PlayerExoActivity::class.java)
                  return PendingIntent.getActivity(
                      context,
                      1,
                      intent,
                      PendingIntent.FLAG_UPDATE_CURRENT
                  )
              }
  
              override fun getCurrentContentText(player: Player?): String? {
                  return "Day " + chapterName
              }
  
              override fun getCurrentContentTitle(player: Player?): String {
                  return courseName!!
              }
  
              override fun getCurrentLargeIcon(
                  player: Player?,
                  callback: PlayerNotificationManager.BitmapCallback?
              ): Bitmap? {
                  return largeIcon
              }
          }
      )
  </code></pre>
  
  <p>This is a receiver to handle other things while Exoplayer state change.</p>
  
  <pre><code>override fun onPlayerStateChanged(playWhenReady: Boolean, playbackState: Int) {
      if (playbackState == ExoPlayer.STATE_BUFFERING) {
          val intent = Intent("com.example.exoplayer.PLAYER_STATUS")
          intent.putExtra("state", PlaybackStateCompat.STATE_BUFFERING)
          broadcaster?.sendBroadcast(intent)
      } else if (playbackState == ExoPlayer.STATE_READY) {
          val intent = Intent("com.example.exoplayer.PLAYER_STATUS")
          if (playWhenReady) {
              intent.putExtra("state", PlaybackStateCompat.STATE_PLAYING)
          } else {
              intent.putExtra("state", PlaybackStateCompat.STATE_PAUSED)
          }
          broadcaster?.sendBroadcast(intent)
      } else if (playbackState == ExoPlayer.STATE_ENDED) {
          val intent = Intent("com.example.exoplayer.PLAYER_STATUS")
          intent.putExtra("state", PlaybackStateCompat.STATE_STOPPED)
          broadcaster?.sendBroadcast(intent)
      }
  }
  </code></pre>