Make array component checking safer

Kenneth Morelandrequested to merge
kmorel/vtk-m:benchmark-num-components into master

One of the checks for BenchmarkFilters is to test the number of components in field arrays. It did this by using a CastAndCall to get the base ArrayHandle and check the type. This is unnecessarily complicated and fragile in the case where the base array type cannot be resolved by CastAndCall. Instead, just query the UnknownArrayHandle for the number of components.

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