Automerge: [NFC][HLSL] Move emitter out of AMDGPU.cpp (#133251)

- Move all HLSL code out of AMDGPU.cpp to CGHLSLBuiltins.cpp
- Fixes accidental reorganization of HLSL code into AMDGPU caused by
(llvm/llvm-project#132252,
llvm/llvm-project@7f920e2e5f70b)

Author: farzonl