[SPIR-V][Feature Request][SM6.5] Add support for FeedbackTexture2D

[Keenuts]

The SPIR-V backend currently doesn't support FeedbackTextures.

Not sure if that's high priority as this support seems optional even on the DirectX side, but creating an issue to track this, and define its priotity.

Texture2D<uint> tex;
SamplerState samplerState;
FeedbackTexture2D<SAMPLER_FEEDBACK_MIP_REGION_USED> feedback;

float4 main() : SV_Target {
  feedback.WriteSamplerFeedback(tex, samplerState, uint2(0, 0));
  uint tmp = tex.Sample(samplerState, uint2(0, 0));
  return float(tmp).xxxx;
}

$ dxc -T ps_6_7 shader.hlsl -spirv
shader.hlsl:6:12: error: intrinsic 'WriteSamplerFeedback' method unimplemented
  feedback.WriteSamplerFeedback(tex, samplerState, uint2(0, 0));

[devshgraphicsprogramming]

Vulkan & SPIR-V is a bit less managed than DX12 & HLSL, I'm not sure same functionality exists in Vulkan

For sample we have no Append/Consume etc.

there's VK_NV_shader_image_footprint but that doesn't give you a thing to write the feedback to, only query the region accessed

emulating this DX12 feature in SPIR-V would require cooperation from the application to supply a BDA ponter, SSBO or Storage Image to use as the feedback and a contract on how to interpret this data

[sudonatalie]

After further investigation, we've decided not to implement this feature in the SPIR-V backend at this time because there is not a solid mapping from DX to Vulkan that would support the full feature's requirements, or most Vulkan end users.

We are open to feedback so additional comments/issues are welcome if this is a high-priority feature for your use case.

Improving the error messaging with #6640