[llvm] [DWARFLinker] Adjust DW_AT_LLVM_stmt_sequence for rewritten line tables (PR #128953)

[Jonas Devlieghere via llvm-commits]

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

When reading the patch I kept thinking "can we pre-compute any of these mappings" but I convinced myself that this is the most efficient approach as we're limiting most lookups to offsets belonging to DIEs that are actually kept. LGTM modulo nits. 

https://github.com/llvm/llvm-project/pull/128953