update_geometry for Open3D scene

### 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).

### Proposed new feature or change

I am building a custom UI which includes a 3D scene. This is why I am using the Open3DScene class instead of Scene class.

However, the former does not have update_geometry for pointclouds. I assume this makes things slow. Can we add update_geometry?

### References

_No response_

### Additional information

_No response_