Request to create and simulate KeyEvents to a window (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](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 would like to simulate input onto an Open3D window in Python. In order to do so I need to be able to create Open3D KeyEvents in Python which is currently not possible. There are obviously work arounds to this which I am using right now, however I think it would be good functionality to have built-in.

### References

_No response_

### Additional information

_No response_