Blender Git Loki

XR: Add "absolute tracking" session setting

Enables users to define the tracking origin in a way that is not
linked to the headset position. Instead, the tracking values given by
the XR runtime are left unadjusted and a user can manually calibrate
an "origin" landmark object to adjust to their real world space.

Can be useful for applications that use external tracking systems
and those that primarily only need to use controllers (e.g. for
motion capture).