Add some of nn.init to weak script (#19640)
Summary:
Stack from [ghstack](https://github.com/ezyang/ghstack):
* **#19640 [jit] Add some of nn.init to weak script**
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19640
Pulled By: driazati
Differential Revision: D15065332
fbshipit-source-id: 30df9f02e527cd5e5ebe34b7e003444eae96c66d