how to use non-block visualization in open3d gui?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](https://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](https://www.open3d.org/docs/release/) and the [latest documentation](https://www.open3d.org/docs/latest/) (for `main` branch).

### My Question

Hi~I've create a window using open3d.visualization.Visualizer.create_window() and add some TriangleMesh or Pointclouds in it, now I wanna add the window to gui to make more interactive function, but I find open3d.visualization.gui.Application.add_window() needs a window that is open3d::visualization::gui::Window type as a input, how can I make that achieved?