[JIT] add id function (#34975)
Summary:
add `id` function so to give uses a way of keeping a `seen` set of nn modules.
n practice, this is only used between values of `T` and `T` or `T` and `Optional[T]`, so in this implementation I made it so that None is the only value that can be zero. Python also only guarantees `id()` gives semantically meaningful results for pointer types.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34975
Differential Revision: D20549677
Pulled By: eellison
fbshipit-source-id: cca5ed4ef013f7540f93abf49f91f9830dfdca14
