Core Support of Virtual Reality Headsets through OpenXR

Implementation of core features needed for XR (virtual, augmented and mixed reality) headsets via the new OpenXR specification (currently in provisional state).

While virtual reality has reached mainstream adoption, it is still not possible to use this technology directly within Blender. There is great potential in the new XR workflows however. This project aims to introduce the core features necessary to build immersive experiences in the Blender viewport through OpenXR. Namely this concerns rendering and interaction with head-mounted displays (HMDs).