Implement visitor pattern for SyntaxTree::Node

[wildmaples]

What, why?

This pattern will expand our horizons and allow us to do fun stuff with the nodes through the SyntaxTree::Visitor class. Right now we are using metaprogramming to create and #send to call our #visit_ methods the LSP. Ideally this would be a built in feature in syntax_tree so others can use it as well.

We've chosen to require the Visitor class in node.rb to make it clearer that the file requires it. Otherwise, we'd have to add it to lib/syntax_tree.rb in an order-dependent way, which we decided was less desirable.

Who

Co-authored-by: Kaan Ozkan [email protected]
Co-authored-by: Alexandre Terrasa [email protected]
Co-authored-by: Vinicius Stock [email protected]
Co-authored-by: Emily Giurleo [email protected]
Co-authored-by: Rafael Franca [email protected]

[kddnewton]

Thank you all so much for the work on this!

Are you relying on visit_method_name in any way or is that just used to make it so that it's easy to do the metaprogramming here?

I think I'd be much more keen to actually write out the visit nodes. The current underscore algorithm feels a little arbitrary. I'd rather we keep the names closer to what ripper has internally since that's what folks coming from Ruby core will know.

That being said, this is a great start, and I'm going to merge it as is for now.