Some fixes to `utils::WriteShapesPovray`:
Some fixes to `utils::WriteShapesPovray`:

- use ChSharedPtr::DynamicCastTo() in order to eliminate double casting (and C-style casting)
- ensure that we only count visual assets that are supported (and written to the output file)

projectchrono/chrono,rserban/chrono,jcmadsen/chrono,jcmadsen/chrono,rserban/chrono,amelmquist/chrono,projectchrono/chrono,armanpazouki/chrono,dariomangoni/chrono,rserban/chrono,jcmadsen/chrono,amelmquist/chrono,armanpazouki/chrono,Milad-Rakhsha/chrono,Bryan-Peterson/chrono,amelmquist/chrono,dariomangoni/chrono,projectchrono/chrono,jcmadsen/chrono,tjolsen/chrono,Milad-Rakhsha/chrono,projectchrono/chrono,Milad-Rakhsha/chrono,tjolsen/chrono,tjolsen/chrono,andrewseidl/chrono,dariomangoni/chrono,armanpazouki/chrono,tjolsen/chrono,andrewseidl/chrono,amelmquist/chrono,tjolsen/chrono,rserban/chrono,armanpazouki/chrono,Bryan-Peterson/chrono,Milad-Rakhsha/chrono,jcmadsen/chrono,Bryan-Peterson/chrono,Milad-Rakhsha/chrono,andrewseidl/chrono,Bryan-Peterson/chrono,rserban/chrono,amelmquist/chrono,Bryan-Peterson/chrono,rserban/chrono,andrewseidl/chrono,dariomangoni/chrono,projectchrono/chrono,dariomangoni/chrono,jcmadsen/chrono,dariomangoni/chrono,armanpazouki/chrono,armanpazouki/chrono,Milad-Rakhsha/chrono,andrewseidl/chrono,rserban/chrono,amelmquist/chrono,projectchrono/chrono,jcmadsen/chrono