Deprecate Execute with policy

The version of Filter::Execute that takes a policy as an argument is now deprecated. Filters are now able to specify their own fields and types, which is often why you want to customize the policy for an execution. The other reason is that you are compiling VTK-m into some other source that uses a particular types of storage. However, there is now a mechanism in the CMake configuration to allow you to provide a header that customizes the "default" types used in filters. This is a much more convenient way to compile filters for specific types.

One thing that filters were not able to do was to customize what cell sets they allowed using. This allows filters to self-select what types of cell sets they support (beyond simply just structured or unstructured). To support this, the lists SupportedCellSets, SupportedStructuredCellSets, and SupportedUnstructuredCellSets have been added to Filter. When you apply a policy to a cell set, you now have to also provide the filter.