Download listening

In UWebView2, these callbacks will be triggered when downloading files, for example, generating table data for users to download.

  void Awake()
  {
      Edge.DownloadStartingEvent.AddListener(OnStart);
      Edge.DownloadProgressEvent.AddListener(OnProgress);
      Edge.DownloadStateChangedEvent.AddListener(OnStateChanged);
  }

  void OnStart(UInt64 task_id, string file_url, string file_save_path, string mime_type)
  {

  }

  void OnProgress(UInt64 task_id, long recvBytes, long total_bytes)
  {

  }

  void OnStateChanged(UInt64 task_id, EdgeWebViewDownloadStateChanged state)
  {
      if(state == EdgeWebViewDownloadStateChanged.COMPLETED)
      {
          // Success
      }
      else
      {
          // Failed.
      }
  }