Merge branch 'point-count' into 'master'

Add PointCount to WorkletMapPointToCell.

WorkletMapPointToCell is a convenience subclass of WorkletMapTopology.
As such, it renames all the From/To signature tags to say Point/Cell to
be easier to read. However, the alias for FromCount was missing. Add the
alias PointCount.

See merge request !303

vtkm/worklet/WorkletMapTopology.h

@@ -189,6 +189,8 @@ public:
   template<typename TypeList = AllTypes >
   struct FieldInOutCell : FieldInOut<TypeList> { };
 
+  struct PointCount : FromCount {  };
+
   struct PointIndices : FromIndices { };
 };