Fix generation of wrap hierarchy files with visual studio generator
This MR fixes a regression introduced by !3694 (merged) and allows VTK to successfully build with Visual Studio generator.
It addresses error like the following:
Error C2440 'static_cast': cannot convert from 'vtkObjectBase *' to 'vtkImagePointDataIterator *' vtkImagingKitPythonD D:\T\VTK-Release\Wrapping\Python\vtkImagePointDataIteratorPython.cxx
Edited by Jean-Christophe Fillion-Robin