[flang] [llvm] [flang][OpenMP] Support custom mappers in target update to/from clauses (PR #169673)

[via llvm-commits]

agozillon wrote:

That's no problem at all! :-) I suppose this PR was primarily waiting on a final approval from @kparzysz I will ask if he has time this week to go over it a final time

https://github.com/llvm/llvm-project/pull/169673