[clang] [clang] Refactor `IdentifierInfo::ObjcOrBuiltinID` (PR #71709)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Yeah, I remember I was able to get past the first round of test failures, only to find another one waiting for me.
Once again I need to sit and debug AST serizalization and deserialization, but I've been occupied with other stuff since then.
I'm not giving up on this just yet, as `ObjCOrBuiltinID ` is an important data member to observe during debugging.

https://github.com/llvm/llvm-project/pull/71709