message: Make the about dialog's contents selectable
diff: @@ -262,7 +262,11 @@ namespace winrt::TerminalApp::implementation
  const auto buttonText = resourceLoader.GetString(L"Ok");
  - _ShowDialog(winrt::box_value(title), winrt::box_value(aboutText), buttonText);
  + Controls::TextBlock aboutTextBlock;
  + aboutTextBlock.Text(aboutText);
  + aboutTextBlock.IsTextSelectionEnabled(true);
  +
  + _ShowDialog(winrt::box_value(title), aboutTextBlock, buttonText);
  }
  // Method Description:
  