[clang-tools-extra] [clang-tidy][NFC] Enable `readability-convert-member-functions-to-static` in the codebase (PR #156265)

[Baranov Victor via cfe-commits]

vbvictor wrote:

I mostly agree with carlosgalvezp, maybe a put this check into the list prematurely, sorry for that.

What I particularly don't like is that it tries to convert `const` members to `static`. I believe if the author intended to use `const`, let him do it. (Maybe we can create an option for it)

> In general I believe static member functions should be a conscious, up-front architectural/design choice

This appears a lot in `TraverseXXX` methods in ASTvisitors. I don't like that they are converted to `static` because semantically, all `Traverse` methods in ASTvisitors should be plain methods.

https://github.com/llvm/llvm-project/pull/156265