[clang] [LifetimeSafety] Run analysis in post-order of CallGraph for better annotation propagation (PR #174178)

[Utkarsh Saxena via cfe-commits]

https://github.com/usx95 approved this pull request.

Overall looks great. Some last nits about the names and using `getDeclWithMergedLifetimeBoundAttrs`to use the common implementation for policy of choosing mostRecentDecl.

https://github.com/llvm/llvm-project/pull/174178