[export] Move attrs to properties and add BC decorator (#106170)
@SherlockNoMad mentioned that it's not bc safe to directly access these attributes, so I moved them to @property fields, and added a `@compatibility` decorator. For now I just set it to True for graph_module/graph.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106170
Approved by: https://github.com/SherlockNoMad
