[llvm] [ctxprof] Move test serialization to yaml (PR #122545)

[Mircea Trofin via llvm-commits]

mtrofin wrote:

### Merge activity

* **Jan 10, 9:02 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/122545).


https://github.com/llvm/llvm-project/pull/122545