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

[Steven Perron via cfe-commits]

https://github.com/s-perron commented:

Thanks for checking with me. To generate better SPIR-V, we should try to use the `OpSDot` instruction when possible. Please use the capability when tageting SPIR-V 1.6 or the extension is available. Thanks.

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