[flang] [llvm] [Flang][OpenMP] Initial defaultmap implementation (PR #135226)

[via llvm-commits]

agozillon wrote:

Thank you very much for the review @skatrak it's greatly appreciated! I've updated the PR now with all of the above changes except the IndexedMap one currently which I've left a comment for my current reasoning! :-)

https://github.com/llvm/llvm-project/pull/135226