feat: JS handles over oxc's tree

js::ast declares bun's handles (Expr, Stmt, Func, Class, Member, Prop,
...) as a file and a node id, and Node::of tells which handle each of
oxc's nodes is. A function or class that is an expression or a
statement is that node, and its Func or Class has the same id, as in
bun's tree. Names are oxc's strings, and a List is a run of siblings
in the table of children.