To serialize an `UnknownArrayHandle`, a pair of lists were created to
specify all possible value and storage types. These were then used in an
`UncertainArrayHandle::CastAndCall`, which would in turn take the cross
of these two lists. This resulted in a _really_ long list that gave
compilers trouble.
Reduce the size of the list by separating out value types by the number
of components, which can be easily deduced.
In VTK-m we have a constant tension between minimizing the number of
types we have to compile for (to reduce compile times and library size)
and maximizing the number of types that our filters support.
Unfortunately, if you don't compile a filter for a specific array type
(value type and storage), trying to run that filter will simply fail.
To compromise between the two, added methods to `DataSet` and `Field`
that will automatically convert the data in the `Field` arrays to a type
that VTK-m will understand. Although this will cause an extra data copy,
it will at least prevent the program from failing, and thus make it more
feasible to reduce types.
Having UnknownArrayHandle.h include DefaultTypes.h is problematic,
because that header includes lots of other classes like cell sets.
Keeping these from in turn depending back on UnknownArrayHandle.h is
difficult. So this dependancy is broken.
