[package] rename ex/importer.py to package_ex/importer.py (#52320)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52320
as title
Test Plan: Imported from OSS
Reviewed By: zdevito
Differential Revision: D26468416
Pulled By: suo
fbshipit-source-id: 890eecea76426918daff900402fbcbc149e48535
