COMP: Fix missing include files

[dzenanz]

Sample error message:

/Users/svc-dashboard/D/Support/ITK-rwdi/Wrapping/castxml_inputs/itkPyCommand.cxx /Users/svc-dashboard/D/Support/ITK-rwdi/Wrapping/castxml_inputs/itkPyCommand.cxx:16:10: fatal error: 'itkPyCommand.h' file not found
   16 | #include "itkPyCommand.h"
      |          ^~~~~~~~~~~~~~~~
1 error generated.

PR Checklist

• [x] No API changes were made (or the changes have been approved)
• [x] No major design changes were made (or the changes have been approved)

[blowekamp]

I would have expected this to be an include path issue?

[dzenanz]

I don't know what is the name of the CMake target, so I would need include_directories. The proposed solution should also have a side benefit of showing these header files in IDEs (Visual Studio, XCode).