Add "work graphs" support

[dzhdanNV]

https://microsoft.github.io/DirectX-Specs/d3d/WorkGraphs.html

[Masihtabaei]

@dzhdanNV

I wrote my thesis on GPU Work Graphs (+ mesh nodes) and sit here in Coburg (a small city in Germany yet with some cool publications utilizing GPU Work Graphs) next to some fantastic Work Graphs experts. I would be really glad to help you add support for Work Graphs (and mesh nodes later) if it is ok for you. I would start with d3d12 since I used it for my all student projects and also my thesis.

[dzhdanNV]

Thanks. There is no WG support in Vulkan yet, thus it's unclear which interface NRI should get.

[dzhdanNV]

Looks like this can be closed as WNI because of microsoft/hlsl-specs#918.