How to initialize O3DVisualizer window in a different location on the screen (Python)

### 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](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

I need to have an O3DVisualizer window appear in a different part of the screen (i.e. window initializes in the top right corner instead of the middle). I haven't found a way to do this using the O3DVisualizer itself or Application.

I'm currently using
> app = o3d.visualization.gui.Application.instance
> app.initialize()
> vis = o3d.visualization.O3DVisualizer("Window", 1000, 700)
> app.add_window(vis)

to create and show the window.