Please support HLSL SV_Barycentrics semantic

I tried to add this support myself but I always hit a wall

I'm targeting SPIR-V code using those extensions:

```
VK_KHR_fragment_shader_barycentric
SPV_KHR_fragment_shader_barycentric
```

and capability:

`FragmentBarycentricKHR`

I patched this file hoping for it to work but it doesn't:

hlslScanContext.cpp
```
(*SemanticMap)["SV_DEPTHGREATEREQUAL"] = EbvFragDepthGreater;
(*SemanticMap)["SV_DEPTHLESSEQUAL"] = EbvFragDepthLesser;
(*SemanticMap)["SV_STENCILREF"] = EbvFragStencilRef;
(*SemanticMap)["SV_BARYCENTRICS"] = EbvBaryCoordEXT;
}

void HlslScanContext::deleteKeywordMap()
```

Start in hlslScanContext.cpp, where HLSL semantics are mapped, and trace how the mapped semantic is lowered for SPIR-V. Check the generated SPIR-V against the requested VK_KHR_fragment_shader_barycentric and SPV_KHR_fragment_shader_barycentric extensions and FragmentBarycentricKHR capability. Done means SV_Barycentrics is accepted and produces the intended SPIR-V output.

Written by the indexing model from the issue text.