[clang] Fix quadratic slowdown in AST matcher parent map generation (PR #87824)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for this, what a great speed-up!

Generally LGTM, though I think you should add a release note to clang/docs/ReleaseNotes.rst so users know about the significant performance improvement.

https://github.com/llvm/llvm-project/pull/87824