The circular dependency came from UnknownArrayHandle.h needing
VTKmDefaultTypes.h, which needed all the cell set types. Some of those
cell sets used ArrayCopy in templated functions. Changed those functions
to directly deep copy the ArrayHandle.
These helper functions were in vtkm::cont::testing, but that made them
hard to discover (and I personally kept forgetting about them). Move
them to the top namespace so that IDE of test_equal will helpfully
remind us of these other test functions.