[clang] [clang] Share RecursiveASTVisitor for AST listing (PR #202661)

[David Zbarsky via cfe-commits]

dzbarsky wrote:

> Looks reasonable to me
> 
> Probably could use with some comments re. what the new `List` mode means
> 
> (attached some possible other reviewers)

thanks, added a comment!

https://github.com/llvm/llvm-project/pull/202661