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

[Jerry Sun via llvm-commits]

jerryyiransun wrote:

Thanks for the feedback, I will review the webpage and make changes accordingly.

> Please also see https://llvm.org/docs/CodingStandards.html#name-types-functions-variables-and-enumerators-properly (@tmatheson-arm made a comment about this but I don't see it). Some of the changes are violating the LLVM's convention for names

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