[clang] [llvm] [HLSL][SPIR-V] Implement vk::location for inputs (PR #169479)

[Nathan Gauër via llvm-commits]

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Keenuts wrote:

Ah good point. Looking into this I also noticed part of the codegen is looking at the triple to determine the shader stage, but it should look at the current function decl.

I'll create another PR to add library test coverage while fixing pre-existing stage mismatch issues. 

https://github.com/llvm/llvm-project/pull/169479