[llvm] [DebugInfo] Add Verifier check for incorrectly-scoped retainedNodes (PR #166855)

[Jeremy Morse via llvm-commits]

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

LGTM with an inline question. Are the test changes manual updates to fix the output of previous (faulty) LLVMs? (Thanks for the maintenance if so!)

https://github.com/llvm/llvm-project/pull/166855