[clang] [llvm] [HLSL][SPIRV][DXIL] Implement `dot4add_i8packed` intrinsic (PR #113623)

[Finn Plummer via cfe-commits]

inbelic wrote:

Rebased to help with resolve merge conflicts.

Thanks a lot for the time and reviews. Really helpful and I learned a lot.

https://github.com/llvm/llvm-project/pull/113623