Resolves#99221
Key points: For SPIRV backend, it decompose into a `dot` followed a
`add`.
- [x] Implement dot2add clang builtin,
- [x] Link dot2add clang builtin with hlsl_intrinsics.h
- [x] Add sema checks for dot2add to CheckHLSLBuiltinFunctionCall in
SemaHLSL.cpp
- [x] Add codegen for dot2add to EmitHLSLBuiltinExpr in CGBuiltin.cpp
- [x] Add codegen tests to clang/test/CodeGenHLSL/builtins/dot2add.hlsl
- [x] Add sema tests to clang/test/SemaHLSL/BuiltIns/dot2add-errors.hlsl
- [x] Create the int_dx_dot2add intrinsic in IntrinsicsDirectX.td
- [x] Create the DXILOpMapping of int_dx_dot2add to 162 in DXIL.td
- [x] Create the dot2add.ll and dot2add_errors.ll tests in
llvm/test/CodeGen/DirectX/
