[llvm] [DWARFLinker][DWARFLinkerParallel][NFC] Refactor DWARFLinker&DWARFLinkerParallel to have a common library. Part 1. (PR #75925)

[Jonas Devlieghere via llvm-commits]

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

Thanks @avl-llvm, LGTM!

https://github.com/llvm/llvm-project/pull/75925