wrap AliasDb in Python (#51336)
Summary:
Also added a wrapper tlemo 's graphviz export to string.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51336
Reviewed By: ezyang
Differential Revision: D26150809
Pulled By: eellison
fbshipit-source-id: 9beafce5cbdc1785b986b71c3cd986c1087faa11
