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

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Finally got past previous test failures. But the following tests started to fail:
```
  Clang :: AST/HLSL/pch.hlsl
  Clang :: PCH/__va_list_tag-typedef.c
  Clang :: PCH/builtin-is-constant-evaluated.cpp
  Clang-Unit :: Lex/./LexTests/failed_to_discover_tests_from_gtest
```
Here is full test output (don't mind `LibClang/symbols.test`, that's my local failure):
https://gist.github.com/Endilll/5d63e138b59af121067d30c77752c437

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