[clang] [clang][NFC] Regroup declarations in `Sema` (PR #82217)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Funny enough, search in the web versions shows only 23 PRs: https://github.com/llvm/llvm-project/pulls?q=is%3Apr+is%3Aopen+%22clang%2Finclude%2Fclang%2FSema%2FSema.h%22

https://github.com/llvm/llvm-project/pull/82217