[clang] [llvm] [NFC][SemaHLSL][CGHLSL] Move semantic classification to common `HLSL/SemanticSignatures` (PR #218058)

[Finn Plummer via llvm-commits]

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inbelic wrote:

There are some other parts of this file that still use the string compare, but they will be cleaned up in https://github.com/llvm/llvm-project/issues/189765

https://github.com/llvm/llvm-project/pull/218058