Provide methods to parse to/from ast.Node from structures

[scr-oath]

It would be convenient even if first pass is implemented as a Marshal to []byte followed by sonic.Get in one direction and MarshalJSON with sonic.Unmarshal in the other, to have methods that interoperate between golang structures and ast.Node

[AsterDY]

You can use ast.NewAny() to construct one from structures ... but now Get/Set on it is not completely supported

[scr-oath]

Yeah, that's not really desired - I guess, if ast is completely disjoint from the rest of the parsing and Pretouch stuff, maybe this isn't easy, but was hoping to avoid the Marshal/Parse to create an ast from an any.