pause method
pause video, it must be called when the player starts playing
视频暂停,必须在播放器开始播放的时候调用
Implementation
@override
Future<void> pause() async {
if (_isNeedDisposed) return;
await _initPlayer.future;
await _vodPlayerApi.pause(PlayerMsg()..playerId = _playerId);
_changeState(TXPlayerState.paused);
}