[llvm] [mlir] [OpenMP][MLIR] Preserve to/from flags in mapper base entry for mappers (PR #159799)

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https://github.com/agozillon approved this pull request.

This looks fine to me, but is there a reason we can't emit the same entries from the frontend as we would if we explicitly mapped map(tofrom: r%real_arr)? As far as I'm aware that mapping should work upstream currently (if it doesn't then it will in the nearish future once the PRs I have up land and I can look into tidying up if at all possible). Just wondering as it'd be nice if we could avoid explicitly specialising the lowering for the mapper, if we can't its fine just curious :-) 

https://github.com/llvm/llvm-project/pull/159799