ENH: Macro expansion for VTK wrappers.
Allow the wrapper's preprocessor to perform macro expansion. Prior to this change, only a few function macros that were hard-coded into the wrappers could be used in the VTK headers. Custom macros would previously cause the wrapper generation to fail. Some macros are not expanded for the sake of backwards compatibility: 1) VTK_* macro constants are not expanded, since these are recognized by some of the later stages of the wrapper processing. 2) vtkDataArray, if defined as a macro, is not expanded in order to allow the vtkDataArrayTemplate superclass trick work as before. 3) All previously hard-coded macros such as the vtkSet/Get macros are still hard-coded for now, to ensure backwards compatiblity Change-Id: I96deec4b9c98badfed88831027011904d197840f