[llvm] [TableGen] [code-cleanup] Refine TableGen code to comply with `clang-tidy` checks and remove unused imports (PR #113318)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

NFC doesn't mean ignorable. They can have a large amount of churn that's significant for blame, and they can end up not being NFC.

https://github.com/llvm/llvm-project/pull/113318