Blender Git Loki

Fix/workaround graphics issues breaking SteamVR use with Blender

Windows only workaround. I'll have to investigate Linux separately.

Steam's OpenGL compatibility is still new and doesn't work for us yet
(neither does it for standard OpenXR examples from what I've heard and
seen myself). We can work around that by falling back to our DirectX
compatibility layer.
Note that this DirectX compatibility still doesn't work for some
systems, see T76082.

Implementation note: Since the graphics binding extensions have to be
enabled before we can find out which runtime is in use (e.g. SteamVR vs.
Oculus, etc), we can now enable multiple graphics binding extensions but
settle for a single one to use later.

Once the SteamVR OpenGL backend works, we can remove this workaround
again.

Fixes T78267.