Run gui.visualization on GPU

### 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

Hi,
I noticed that whenever I open a point cloud file inside a `o3d.gui.visualization` window, some being significantly large (+2mil points), that panning and rotating is not performing smoothly (lagging a lot).

When I open the `ml3d.visualizer` I notice that panning and rotating inside this application is running way smoother than the `o3d.gui.visualization`. The `ml3d.visualizer` is setup for CUDA usage.

I believe that it has something to do with device usage (CPU or GPU). Is there a way I can enable the `o3d.gui.visualization` to be executed using my GPU?

I would like to use the `o3d.gui.visualization` since this allows for more modifications.

I hope someone is able to give me some advice!
Thanks in advance!
Richard

The entry points named are o3d.gui.visualization and ml3d.visualizer; begin by comparing how each handles GPU or CUDA usage and checking the relevant documentation. Done means the supported GPU behavior for o3d.gui.visualization is established and the large point-cloud interaction case is addressed or its limitation is clearly documented.

Written by the indexing model from the issue text.