I'm embedding a 3D viewport inside GPUI by creating a child window with its own surface that fits the bounds of a GPUI element, and I need access to the raw window handle of the current window to manage it. Right now on X11 this is stubbed as unimplemented and results in a panic. I've copied most of the same implementation from the associated `RawWindow` into `X11Window`. Small clip of a Bevy app embedded inside GPUI with a popover that draws above the 3d surface to show testing was done: [Screencast_20260304_182657.webm](https://github.com/user-attachments/assets/829f9197-1613-41a7-af83-d377f3154751) Before you mark this PR as ready for review, make sure that you have: - [x] Added a solid test coverage and/or screenshots from doing manual testing - [ ] Done a self-review taking into account security and performance aspects - [ ] Aligned any UI changes with the [UI checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist) Release Notes: - Added implementations of `rwh::HasDisplayHandle` and `rwh::HasWindowHandle` for `X11Window`