[SPIR-V][Feature Request][SM6.7] Implement SampleCmpLevel

[Keenuts]

SM6.7 added SampleCmlLevel which is similar to SampleCmp, but which fixes the LOD at which the comparison is done.

Texture2D<float> tex;
SamplerComparisonState samplerComparisonState;

float4 main() : SV_Target {
  float tmp = tex.SampleCmpLevel(samplerComparisonState, float2(0, 0), 2, 3);
  return tmp.xxxx;
}

$ dxc -T ps_6_7 shader.hlsl -spirv -fspv-target-env=vulkan1.3
shader.hlsl:7:19: error: intrinsic 'SampleCmpLevel' method unimplemented
  float tmp = tex.SampleCmpLevel(samplerComparisonState, float2(0, 0), 2, 3);

Seems like this could be implemented with a small change in DXC: SampleCmpLevelZero uses the correct instruction, but fixes the LOD to 0. But passing a register is possible, so seems like implementation will be straightforward.