[llvm] [DebugInfo][DWARF] Utilize DW_AT_LLVM_stmt_sequence attr in line table lookups (PR #123391)

[via llvm-commits]

alx32 wrote:

@dwblaikie - I think either way is fine. The reason it's like this currently is because the `stmt_sequence` offset is somewhat specific/internal to the line table format so it might make more sense for the line table to query it directly from the DIE. But you're right the line table had so far no knowledge of DIEs up until now. 

Also if multiple callers will be reusing this functionality they'll have to separately query for the attribute having a bit of duplicate code.

I'll change the API to take an offset in a bit if no one else has a strong preference otherwise. 

https://github.com/llvm/llvm-project/pull/123391