Make nn.Module `forward()` type annotation more permissive (#31057)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31057
The current signature basically will always fail to type check, because
mypy enforces that the subclass method's input types must be "wider"
than their superclass method's input types (i.e. they can vary
contravariantly). And nothing is wider than `Any`.
This change makes it so that any input params are allowed in
`forward()`. Fixes #29099
Test Plan: Imported from OSS
Differential Revision: D18918034
Pulled By: suo
fbshipit-source-id: 9940e9f769b55d580d9d7f23abf6f88edb92627f
