OpenXR Overlay Support

[bwRavencl]

To support VR overlays in applications that use OpenXR (e.g. Microsoft Flight Simulator) an overlay implementation is required analogously to the current OpenVR implementation.

Links:

• https://steamcommunity.com/app/250820/discussions/8/3041607080046568983/
• https://www.khronos.org/registry/OpenXR/specs/1.0/html/xrspec.html#XrSessionCreateInfoOverlayEXTX
• https://github.com/LunarG/OpenXR-OverlayLayer
• https://www.reddit.com/r/OpenXR/comments/rk0eg2/does_openxr_support_overlay_apps_the_way_steamvr/
• https://github.com/mbucchia/OpenXR-Toolkit
• https://github.com/fredemmott/OpenKneeboard/tree/master/docs/internals
• Add OpenXR Support OpenKneeboard/OpenKneeboard#9
• https://javadoc.lwjgl.org/org/lwjgl/openxr/EXTXOverlay.html
• https://registry.khronos.org/OpenXR/specs/1.0/loader.html#api-layer-interaction
• https://fredemmott.com/blog/2022/05/31/in-game-overlays.html