[clang] [llvm] [HLSL][SPIRV] Support Flat and Location decorators in the frontend (PR #210116)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

> Do we want to require the same decoration be added within the context of a library shader? 

There  wouldn't be decorations to the library shaders.

> In this case, the target is library, yet we could be processing a pixel shader function with the pixel shader attribute. Separately, it might be worth adding a library case to document / test this behavior

While i'm not explicitly testing that the attribute is not applied, i did notice  during development of this pr that before I limited the change via `ShaderAttr->getType() == llvm::Triple::EnvironmentType::Pixel` I was getting test failures.  So I don't think we need an explicit these attributes are not here test, but  can add one if you feel strognly about it.



https://github.com/llvm/llvm-project/pull/210116