[llvm] [DXIL] Add constraint specification and backend implementation of DXIL Ops (PR #97593)

[S. Bharadwaj Yadavalli via llvm-commits]

https://github.com/bharadwajy commented:

Changes that use `list` in place of `dag` pushed - per PR feedback. 

Will update the design document in accordance with these changes in a separate PR after this implementation PR is merged.

https://github.com/llvm/llvm-project/pull/97593