Fix #1115: Enrich js.WrappedArray with Buffer and BufferLike.

This basically turns it into a full-blown Scala collection,
whose implementation happens to use a js.Array.

We also mark it @inline, because it gives the BufferLike
interface to js.Array, which js.ArrayOps cannot provide due to
the type parameters of BufferLike being too restrictive.
Specialize genTraversableOnce2jsArray for js.ArrayOps and js.WrappedArray.

In a sense, this is as if .toJSArray were overridden in js.ArrayOps
and js.WrappedArray, which makes total sense. But since .toJSArray
is a pimp, we need to make this specialization directly in its
implementation.