Blender Git Loki

Ghost: Support drawing OpenGL framebuffers into a DirectX 11 buffer

Adds a minimal DirectX 11 Ghost context, plus some shared DirectX-OpenGL
resource interface using the NV_DX_interop2 WGL extension. From what I
know, this should be available on modern GPUs. If not, it should fail
gracefully.
There should be no user visible changes at this point.

Needed for DirectX-only OpenXR platforms (e.g. Windows Mixed Reality). I
heard there are other use-cases as well though.

It's known that this currently fails on some AMD systems, but that seems
to be fixable.

Most of this comes from the 2019 GSoC project, "Core Support of Virtual
Reality Headsets through OpenXR"
(https://wiki.blender.org/wiki/User:Severin/GSoC-2019/).

Reviewed by: Jeroen Bakker, Ray Molenkam, Brecht van Lommel

Differential Revision: https://developer.blender.org/D6190