[clang] [Sema][Serialization] Emit unused local typedefs in a deterministic order (PR #209639)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

I added the serialization maintainers for their opinions, but I think this is generally a reasonable idea. It will need a release note in `clang/docs/ReleaseNotes.md` so users know about the fix, though.

https://github.com/llvm/llvm-project/pull/209639