[FSDP] Enforce wrapper_cls as a mandatory kwarg in enable_wrap. (#69358)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/69358
Enforces and raises error earlier if wrapper_cls is not provided as an
arg into enable_wrap() function. Also improves the documentation.
ghstack-source-id: 144807950
Test Plan: CI
Reviewed By: zhaojuanmao
Differential Revision: D32826963
fbshipit-source-id: d1b98df021e86d3d87a626e82facf6230b571a55
