Refactor SavedVariable (#59836)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59836
Preparing for #58500
Test Plan: Imported from OSS
Reviewed By: ailzhang
Differential Revision: D29069159
fbshipit-source-id: dd4d870c8ae10a4bd7f12be127e093f60fa072fa
