[clang] [mlir] [MLIR][OpenMP] Add OpenMP_IntLikeTypeInterface to allow other dialect inputs to omp ops (PR #196363)

[Henrich Lauko via cfe-commits]

xlauko wrote:

I would think of `UnrealizedConversionCastOps` surviving multiple steps not really idomatic, they are meant to just note "here is some conversion that needs to be hadeled in this pass", ideally in between passes you sould have IR that has some expected form. 

On the other hand why `OpenMP_IntLikeTypeInterface` and not introducing this to core mlir similarly to floats and pointers? Then arbitrary consumer of CIR can use the interface not just OpenMP.

Also present solution would require attaching `OpenMP_IntLikeTypeInterface` to CIR types which creates not nice dependency direction in my opinion.

https://github.com/llvm/llvm-project/pull/196363