Convert constant and affine arrays to Viskores

Previously, if a dataset field was represented by a vtkConstantArray or a vtkAffineArray, the entire conversion process would fail. The Viskores data converters now properly convert vtkConstantArray to viskores::cont::ArrayHandleConstant and vtkAffineArray to either viskores::cont::ArrayHandleIndex or viskores::cont::ArrayHandleCounting.

This fixes problems seen in ParaView where the LOD conversion throws a warning (and reverts to a serial algorithm) in instances like multi-block datasets. These datasets often have constant arrays to identify blocks within each partition.

The code is also updated to just issue a warning and continue conversion when an array of unknown type is encountered. This means the Viskores algorithm will still run, but the fields with 「weird」 array types will get dropped.