GPU support for open3d.t.geometry.RaycastingScene?

### 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

According to open3d.t.geometry.RaycastingScene, it only supports CPU device.
Are there any plans to add GPU support for ray casting using a mesh?

Start with the open3d.t.geometry.RaycastingScene API and its documentation to understand the current CPU-only behavior. Investigate the existing ray-casting entry points and GPU-related parts of Open3D, then determine the scope and design needed for mesh ray casting on the GPU; the issue does not define a concrete completion criterion or name implementation files or tests.

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