[OpenMP][5.1] Support `thread_limit` on `omp target`

It is unclear to me what happens if we have two thread_limit clauses to
choose from. I will recommend to the standards committee to disallow
that. For now, we pick the teams one.

Fixes https://github.com/llvm/llvm-project/issues/59940

Differential Revision: https://reviews.llvm.org/D141540