[clang] [Clang] [NFC] Introduce `ConstDynamicRecursiveASTVisitor` (reland) (PR #124821)

[via cfe-commits]

cor3ntin wrote:

> > I really hope we're not in a situation where we need the `template` for some bots and can't have it for other bots.
> 
> Yeah, that’s what I’m a bit worried about too...

Well, at worst

```cpp
using Base = RecursiveASTVisitor<Impl<Const>>; // and you can put that at class level
return Base::Function(...);
```

https://github.com/llvm/llvm-project/pull/124821