[FX] Pickle serialization of GraphModule via forward source (#43674)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/43674
Test Plan: Imported from OSS
Reviewed By: dzhulgakov
Differential Revision: D23362396
Pulled By: jamesr66a
fbshipit-source-id: cb8181edff70643b7bbe548cc6b0957328d4eedd
