Reflect GLSL PS interpolation qualifiers about slang

[tangent-vector-personal]

Are you just referring to things like the sample qualifier on fragment shader varying inputs:

sample vec2 whatever;
centroid vec4 somethingElse;

Or are there more requirements beyond that? E.g. do you need to be able to test if the shader uses the gl_SampleIndex built-in variable, or anything like that?

How does the situation for Vulkan differ from D3D?

[nbentyNV]

I need to know if the shader requires us to use super-sampling, similar to ID3D12ShaderReflection::IsSampleFrequencyShader()

In DX12, supersampling is enabled automatically if the PS use any inputs that are evaluated at sample location or SV_SampleIndex is used.
In Vulkan we have to enable super-sampling in the rasterizer state, otherwise the FS declarations will be ignored.

[tangent-vector]

There is now a basic version of this in place thanks to PR #79.

Leaving this open in case it doesn't meet requirements.