[llvm] [dsymutil] Adjust the debug map object filter (PR #219846)

[Jonas Devlieghere via llvm-commits]

https://github.com/JDevlieghere commented:

Giving DebugMap its own independent iterators makes it a line-for-line duplicate of DebugMapFilter's own block (lines ~53-66), differing only in element type. I'm leaning towards the alternative you mentioned in the PR description of using something like `DebugMapFilterBase<T>`.

https://github.com/llvm/llvm-project/pull/219846