Add `save()` to `torch._C.Function` (#20386)
Summary:
Fixes #20017
This wraps the `torch._C.Function` currently returned from `torch.jit.script` and `torch.jit.trace` in a `ScriptFunction` and `TracedFunction` respectively, both of which are just wrappers to hold the function.
](https://our.intern.facebook.com/intern/diff/15403161/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20386
Pulled By: driazati
Differential Revision: D15403161
fbshipit-source-id: 94fb9f32929e62a00be6cf7512ea144ec9b91e0b
