[flang] [llvm] [mlir] [flang] Add support for workdistribute construct in flang frontend (PR #146029)

[via llvm-commits]

skc7 wrote:

> I think this PR can be split into 2: one for parsing and one for lowering from PFT to MLIR.
> 
> Also, we are still missing tests for parsing AFAICT.
> 
> Do we have a PR for semantic checks? Or are we planning to do that in a later PR?

Thanks @ergawy for feedback. Will re-evaluate and work on changes.

https://github.com/llvm/llvm-project/pull/146029