Use dataclasses to simplify ShardingSpec (#58893)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58893
Leverage dataclasses to simplify some of the ShardingSpec classes.
ghstack-source-id: 130041687
Test Plan: waitforbuildbot
Reviewed By: SciPioneer
Differential Revision: D28665137
fbshipit-source-id: da37517cf2bd8c65d4a5b7cae171fa460e6b0946
