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

[Paul C. Anagnostopoulos via llvm-commits]

Paul-C-Anagnostopoulos wrote:

I'm not actively working on TableGen these days, so you don't really need my opinion. But these cleanups are a great idea and so go for it.

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