message: New onConnectionEnd() callback
  Summary: To combine connection close callbacks with or without errors.
diff: @@ -111,6 +111,13 @@ class QuicSocket {
  */
  virtual void onConnectionError(QuicError code) noexcept = 0;
  + /**
  + * Invoked on transport closure. No callbacks will be delivered after this.
  + * onConnectionEnd() and onConnectionError(QuicError code) will be
  + * deprecated in favor of this new combined callback soon.
  + */
  + virtual void onConnectionEnd(QuicError /* error */) noexcept {}
  +
  /**
  * Called when more bidirectional streams become available for creation
  * (max local bidirectional stream ID was increased).
  