[llvm] [DXIL] Model DXIL Class specification of DXIL Ops in DXIL.td (PR #87803)

[Damyan Pepper via llvm-commits]

https://github.com/damyanp approved this pull request.

It'd be good to be clear on how errors are handled/reported. Is assert the right thing to use in all cases here?

https://github.com/llvm/llvm-project/pull/87803