make visualization apis more consistent

for 3d viz, the call is `from openfe.utils.visualization_3D import view_mapping_3d`

whereas for 2d viz, you use `atom_mapping.draw_to_file()`. 

we should decide on a unified API for all atom mapping visualization.

@IAlibay you originally brought this up, so I'm curious if there are additional criteria or requests you have before I propose an api.