Previously, WorkletPointNeighborhood had a template argument to select
the size of the neighborhood. This change removes that template
argument. Instead, the vtkm::exec::arg::BoundaryState methods now take
in a size parameter when determining when it overlaps the boundary.

If in the future we want to add the ability to select the neighborhood
size at compile-time (for performance reasons), I suggest adding this
template argument to the OnBoundary tag for ExecutionSignature.