message: clear selection on viewport/font resize
  ## Summary of the Pull Request
  Match conhost behavior and clear selection on viewport/font resize.
  ## PR Checklist
  * [X] Closes
  ## Validation Steps Performed
  Retried attached bug repro steps
diff: @@ -1499,6 +1499,8 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
  return;
  }
  + _terminal->ClearSelection();
  +
  // Tell the dx engine that our window is now the new size.
  THROW_IF_FAILED(_renderEngine->SetWindowSize(size));
  