The original design of invoke and the transport infrastructure
relied on the implementation behavior of vtkm::cont types
such as ArrayHandle that used an internal shared_ptr to managed
state. This allowed passing by value instead of passing by
non-const ref when needing to transfer information to the device.

As VTK-m adds support for classes that use virtuals the ability
to pass by base pointer type allows for us to invoke worklets
using a base type without the risk of type slicing.

Additional by moving over to a non-const ref Invocation we
can update all transports that have 'output' to now be
by ref and therefore support types that can't be copied while
being 'more' correct.