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

[Krzysztof Parzyszek via llvm-commits]

kparzysz wrote:

The changes themselves are fine.  Such large-scale commits are usually avoided, but we've gone through various renaming efforts in the past.  I'm fine with committing this, but let's check with @Paul-C-Anagnostopoulos.

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