Implement XrGraphicsBindingEGLMNDX instance extension

[kwahoo2]

Hi,

If I understand correctly, to run an OpenXR app in Linux/Wayland (with Monado or SteamVR) XrGraphicsBindingEGLMNDX is required. It is provided by XR_MNDX_egl_enable

xr-video-player implementation can give some hints https://codeberg.org/yoshino/xr-video-player/src/branch/master/src/main.cpp#L808