Refactor vtkDataSetTriangleFilter for better performance.
This refactors vtkDataSetTriangleFilter and vtkHexahedron for better performance. For vtkStructuredGrid inputs, it also lowers memory consumption by creating a shallow copy of the points array.
1.8 GB vtkStructuredGrid with cell blanking this branch: 32 s master: 43 s VTK v7.1.0: 59 s