Blender Git Loki

Use OpenXR extension for extra debug messages in debug mode

Enables (or tries to) the XR_EXT_debug_utils extension which allows
setting a custom callback for additional debug prints. Note that I
haven't been able to test this really, as the Monado runtime appears to
not have this fully implemented (had to force sending a custom message
to find that out...). Will test with the Windows MR runtime in a bit. We
can also improve message quality then (it can print the exact function
name the message was sent from, print additional custom labels which
could indicate session state, etc.).