[lld] [lld-macho][NFC] Refactor ObjCSelRefsSection => ObjCSelRefsHelper (PR #86456)

[Kyungwoo Lee via llvm-commits]

https://github.com/kyulee-com approved this pull request.

LGTM. It appears this was my original comment on not inheriting SyntheticSection, although I was not sure about this potential issue.
BTW, this is still a draft PR, and you might want to publish it so that everyone can see this PR.

https://github.com/llvm/llvm-project/pull/86456