Condense vtk sources to have one output port

Originally, VTK sources for SMTK resources had three output sources: one for components, one for instance prototypes and one for instance placements. A single instance of the consuming vtkSMTKResourceRepresentation would then ideally connect to these three ports. ParaView's default behavior resulted in the creation of an instance of the representation class for each port, however, resulting in duplicate rendering of instance prototypes as components (in addition to other rendering artifacts, such as z-fighting).

The new design passes component multiblocks, instance prototypes and instance placements via a single port as a multiblock with three blocks. The consuming representation now extracts each of the three blocks and renders them appropriately.