Blender Git Loki

Extern: Add TinyGLTF to load XR controller model

The XR_MSFT_controller_model OpenXR extension provides a glTF
controller model that can be displayed to users during a VR session.
There are plans to support this in D10948, which will greatly improve
VR immersion when using a compatible OpenXR runtime.

TinyGLTF (https://github.com/syoyo/tinygltf) was agreed upon as a
simple and sufficient solution for loading this glTF controller model,
which will be performed at the GHOST abstraction layer. Although by
default it has two additional dependencies, stb and json, stb can be
excluded by defining TINYGLTF_NO_STB_IMAGE and
TINYGLTF_NO_STB_IMAGE_WRITE whereas json will be added as a separate
extern lib in D12567.

Reviewed By: Severin

Differential Revision: https://developer.blender.org/D12344