Make `js.Array` a Scala object instead of a native JS object.
Make `js.Array` a Scala object instead of a native JS object.

The main reason is that its `apply` method is a primitive, and JS
types should not contain primitive methods.

Additionally, this opens the door to add more Scala collection-like
methods on that object, such as an `empty` method.

nicolasstucki/scala-js,scala-js/scala-js,SebsLittleHelpers/scala-js,gzm0/scala-js,scala-js/scala-js,sjrd/scala-js,sjrd/scala-js,nicolasstucki/scala-js,sjrd/scala-js,SebsLittleHelpers/scala-js,gzm0/scala-js,scala-js/scala-js