[milestone] Pixel and Vertex Shaders

[damyanp]

TODO: refine this milestone description. Roughly, this milestone tracks that most common pixel and vertex shader functionality is present.

Workstreams

Language (#21)

• Barycentric Design

Semantics (#25)

• Semantics on fields in structure arguments
• Structure flattening and semantic assignment for Signature Elements
• Generate input/output translation for entry wrapper

Resources (#8)

• Sampler Feedback

DirectX Container (#9)

• Entry properties for vertex and pixel shader in PSV0 part.
• [DirectX] DXContainer support for SM 6.8 feature flags llvm-project#83177