move helper functions out of Partitioner class (#47515)
Summary:
This PR moves some helper functions out of Partitioner class. It will make Partitioner class cleaner and make these helper functions easier to use in the future
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47515
Reviewed By: gcatron, heitorschueroff
Differential Revision: D24844751
Pulled By: scottxu0730
fbshipit-source-id: 04397d0ce995cf96943df0a2b9265a521177b4de
