[MLIR][OpenMP] Update omp.wsloop translation to LLVM IR (4/5) (#89214)

This patch introduces minimal changes to the MLIR to LLVM IR translation
of `omp.wsloop` to support the loop wrapper approach.

There is `omp.loop_nest` related translation code that should be
extracted and shared among all loop operations (e.g. `omp.simd`). This
would possibly also help in the addition of support for compound
constructs later on. This first approach is only intended to keep things
running after the transition to loop wrappers and not to add support for
other use cases enabled by that transition.

This PR on its own will not pass premerge tests. All patches in the
stack are needed before it can be compiled and passes tests.