Fix RenderingTk compilation

The vtkTkAppInitConfigure.h header would not compile because it used the VTK_ABI_NAMESPACE macros without including the header that defined them. This wasn't caught because RenderingTk is not part of the CI testing.

For proper testing, two things are needed:

1. enable the RenderingTk module on linux (installing Tk on other platforms is tricky)
2. ensure that vtkLoadPythonTkWidgets.py can find the libvtkRenderingTk-X.Y.so Tk extension module

The following tests already exist for RenderingTk:

VTK::FiltersSourcesPython-squadViewer
VTK::RenderingTkPython-cursor3D
VTK::RenderingTkPython-TestTextActor3D
VTK::RenderingTkPython-TestTkRenderWidget
VTK::RenderingTkPython-TestTkRenderWindowInteractor