After the change to `ArrayHandleVirtual` where it became a subclass of
`vtkm::cont::ArrayHandle`, a few extra changes are required.
1. Functions with `ArrayHandleVirtual` as parameters will not be callable
with the superclass `ArrayHandle`. This is fixed by changing the argument
types to the superclass.
2. Add Serialization classes specializations for the superclass, as "is-a"
relation is not considered for class template parameters.
Previously, ArrayHandleVirtual was using the default Transfer object.
This was problematic because it would copy/allocate things in the
execution environment independently from the array that it was wrapped
around. This caused several negative effects, particularly for CUDA
devices. First, if the data were already on the device (or the array is
implicit), a second copy of the data would be made. Second, the copy to
the device is likely less efficient. Third (and worst of all), the data
did not always get pulled back to the original array correctly.
This commit also contains instantiations of ArrayHandleVirtual and its
components for the most common types.
Previously, ArrayHandleVirtual was defined as a specialization of
ArrayHandle with the virtual storage tag. This was because the storage
object was polymorphic and needed to be handled special. These changes
moved the existing storage definition to an internal class, and then
managed the pointer to that implementation class in a Storage object
that can be managed like any other storage object.
Also moved the implementation of StorageAny into the implementation of
the internal storage object.
Previously these two functions would give compile errors when asked to
compare against an Array with a different value type. This makes it easier
to write generic code that compares virtual handles.
ArrayHandleVirtual can automatically be constructed from any ArrayHandle.
In the cases where the input ArrayHandle doesn't derived from ArrayHandleVirtual,
it will automatically construct StorageAny to hold the array.
