Add CastAndCallScalarField and CastAndCallVecField to NewFilterField

Kenneth Morelandrequested to merge
kmorel/vtk-m:cast-and-call-field into master

These methods somewhat simplify doing the CastAndCall from an UnknownArrayhandle that comes from an input field.

The motivation for this change is for the User's guide, where I am having a chicken-and-egg problem of wanting to describe how to make a simple filter implementation without having to go into details about UnknownArrayHandle.

Also updated the CrossProduct filter to the new filter structure, which provides a demonstration of CastAndCallVecField.

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