[package] Allow save_module to accept module as arg (#55996)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55996
**Sumamary**
This commit modifies `PackageExporter.save_module` so that the `module`
argument can be either a string (`str`) or a module
(`types.ModuleType`).
**Test Plan**
This commit adds a unit test similar to `TestSaveLoad.test_save_module`
that tests that calling `save_module` with a module object works.
**Fixes**
This commit fixes #55939.
Test Plan: Imported from OSS
Reviewed By: jamesr66a, huiguoo
Differential Revision: D27771781
Pulled By: SplitInfinity
fbshipit-source-id: 57c8cf45575bb8dcfca711759fadfff72efb35e7
