Old VTK modules aren't importing vtkRenderingOpenGL2

The vtk.wxVTKRenderWindow used to import "vtk" to bring in the OpenGL backend, but since the code was modified to use "vtkmodules", the vtkRenderWindow no longer has an implementation (See #18347 (closed)). The same is probably true for other Python modules that haven't been tested recently.

Adding this issue to remind myself to examine these modules (though I'm not set up to test all of them).

The fix is to add import vtkRenderingOpenGL2, import vtkRenderingUI, import vtkRenderingFreeType, and import vtkInteractionStyle where appropriate.