Fix transparency by propagating property keys to parts of vtkPropAssembly

I experienced similar problems as described in https://discourse.vtk.org/t/translucent-assemblies-in-8-2-0/419/8 which have been addressed by !5312 (merged). (@allisonvacanti @ken-martin have been involved).

The issue mentioned above was about rendering of vtkAssembly objects. In my case I was using vtkPropAssembly. Rendering vtkPolyData objects via a vtkPropAssembly using dual depth peeling was giving me results like this:

I attempted applying the logic of the fix for vtkAssembly: vtkPropAssembly now propagates property keys to its part in the different rendering methods. With those changes rendering is corrected and looks like expected:

Please let me know if if additional information or changes are required.