[package] properly handle case where we are re-packaging mocked modules (#61434)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61434
Mocking is the only time we introduce a "special" module to a
torch.package of our own creation. This interacts poorly with
re-packaging, since if we treat `_mock` as a regular module and try to
package it normally we will produce a broken package.
This PR teaches PackageExporter to recognize `_mock` modules and treat
them specially during the dependency walking process, thus avoiding the
issue.
Test Plan: Imported from OSS
Reviewed By: jdonald, Lilyjjo
Differential Revision: D29638283
Pulled By: suo
fbshipit-source-id: 37a7ffa34da8bb665f679fbd72aa3d71154b2209
