[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:

> What’s the best way to do this? Split it per file?

The issue is that "formatting" commits introduce noise in the file history, which can affect things like `git blame`.  There are ways around it, for example, blame allows you to give a list of commits to ignore (we have it in `.git-blame-ignore-revs`), but you still have to manually provide that option.  Some tools may not be doing it, and so they can trace some change back to an NFC commit.

The "preferred" approach it to tack it on top of some functional commit, i.e. make such changes to the code that the commit was changing anyway.  The downside is that this process may never finish all the intended changes.

Paul is the code owner of TableGen, so I defer to him to make the final decision.  This change is fine if there is a consensus to do it, and I'm not opposed.

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