ImplicitArray: NewInstance to give explicit AOS arrays

Although coutnerintuitive, changing the NewInstance behavior of implicit arrays corresponds to more use cases then their current behavior. The most common use of NewInstance in VTK is to create an empty instance of an object and populate it with some filtered data. In the case of implicit arrays, this population step is not possible since they are read only. Return AOS arrays allows most use cases to just work out of the box.