Add smart debugging function for `GreenNodeBuilder`

[K4rakara]

As it is, debugging issues with GreenNodeBuilder isn't easy. Sure, you can dbg! it, but it doesn't label what the SyntaxKinds are, rather, it just displays them with their raw value.

I think it would be great to add a function that helps with this. Ideally it would log something like this:

Root@0..21
    Member@0..21
        Public@0..3 "pub"
        Ignore@3..4 " "
        TypeAlias@4..21
            Ignore@4..8 "type"
            Ignore@8..9 " "
            TypeAliasName@9..12
                Ident@9..12 "Foo"
            Ignore@12..13 " "
            Ignore@13..14 "="

The last node (and/or token) would likely be highlighted in green to signify that it is the current node.

If this would be a welcome addition, I would be more than happy to implement it, but I wanted to ask first.