[clang] [PAC] Implement function pointer re-signing (PR #98847)

[Daniil Kovalev via cfe-commits]

https://github.com/kovdan01 commented:

I've left a bunch of mostly cosmetic comments and minor nits which are non-blocking in terms of merging that. However, I'll take another look at this "with fresh eyes" within a day - I need a bit more time to drill into actual logic.

https://github.com/llvm/llvm-project/pull/98847