Handler for unknown nodes

[brettz9]

Hi,

I've made an experimental parser to support treating JSDoc blocks as full-blown nodes. I adjust the visitor keys of regular nodes to accept a jsdoc property which holds the structured AST (or in the case of Program, a jsdocBlocks array of JSDoc AST for the sake of unattached comments).

I'm wondering if you might be open to providing a mechanism such that either you optionally support these experimental nodes if you think this may be something of wider interest, or so that one could customize the printing behavior, e.g., to pass in one's own stringifiers.

It looks like there was openness expressed at benjamn/ast-types#286 (comment) , and a connected issue at #219 , but as that looks to be more about customizing the style of printing rather than a fallback for unknown nodes, I thought I'd file this to express my wish for such a use case.

Thanks!