[clang] [NFC] Minimize header includes (PR #66339)

[Anders Waldenborg via cfe-commits]

https://github.com/wanders approved this pull request.

LGTM.

Assuming that clang/examples/Attribute/ still compiles fine  (it should be part of clang/test/Frontend/ tests)

https://github.com/llvm/llvm-project/pull/66339