This PR allows the OpenXRHand to drive:
- OpenXR rigged hand skeletons located under the OpenXRHand node
- Godot Humanoid rigged hand skeletons located under the OpenXRHand node
- OpenXR rigged avatar skeletons located separately in the scene-tree
- Godot Humanoid avatar skeletons located separately in the scene-tree
We don't use that info for anything, and it generates unnecessary diffs
every time we bump the minor version (and CI failures if we forget to
sync some files from opt-in modules (mono, text_server_fb).
