feat: JS declaration handles

decl.rs maps oxc's functions, classes, members, properties,
parameters, interfaces, aliases, enums, namespaces, imports and exports
to bun's handles. Keyword modifiers are flags in oxc, so modifiers()
lists only decorators. A rest parameter and an index signature's
parameter are Params, and namespace A.B {} is one node, as in bun.
js::strings has the string helpers of bun's that the printer uses.