add submodules to sys.modules so their attributes can be pickled (#53107)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/38137
As mentioned in the issue, this is a workaround for [python issue 43367](https://bugs.python.org/issue43367). There are a number of other places where `sys.modules` is modified, if something changes in python perhaps those should be reviewed as well.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53107
Reviewed By: zou3519
Differential Revision: D26753571
Pulled By: ezyang
fbshipit-source-id: 2bda03bab39ff9ca58ce4bc13befe021da91b9c4
