[clang] [LifetimeSafety] Revamp test suite using unittests (PR #149158)

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

### Merge activity

* **Jul 22, 10:30 AM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/149158).


https://github.com/llvm/llvm-project/pull/149158