[clang] [llvm] [HLSL][DXIL][SPIRV] Create llvm dot intrinsic and use for HLSL (PR #102872)

[Greg Roth via cfe-commits]

https://github.com/pow2clk commented:

The three commits are independently committable, but this is the grouping @farzonl and I agreed on. Reviewing them individually still might make this easier: 

1. Create llvm dot intrinsic (6fde4bc98d0156024cf7acc27e2e986b9bec3993)
2. Update DX intrinsic expansion for new llvm intrinsics (7ca6bc5940321c18f5634bb960fa795366097e45)
3. Add SPIRV generation for HLSL dot (490c0c05c5762a622d037b472c85234ce3f39c96)

https://github.com/llvm/llvm-project/pull/102872