Previously, the conversion from a `vtkm::cont::UnknownArrayHandle` to a
`vtkDataArray` relied on the array being a known `Vec` size. This
restriction has been lifted, and tuples of any size can be converted
from an `ArrayHandleBasic` or an `ArrayHandleSOA` to an
`vtkAOSDataArrayTemplate` or `vtkSOADataArrayTemplate`, respectively.

The code is also more clever about when to copy data to VTK. It avoids
transferring the data if it means copying data from device to host.