`VaraintArrayHandle` has been replaced by `UnknownArrayHandle` and
`UncertainArrayHandle`. Officially make it deprecated and point users to
the new implementations.
Implement more general versions of `test_equal_ArrayHandles`, `test_equal_CellSets`, `test_equal_Fields`, and `test_equal_DataSets` functions and put them
in vtkm/cont/testing/Testing.hi with the hope that they will be useful for
others also.