Add support for vmap+fwdAD for basic out-of-place op (#66291)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66291
In this PR:
- Trivial batching rules for `make_dual` and `is_same_size` that enable forward ad + vmap functionality
- Adds a check in gradcheck that is performed when both `check_batched_grad` and `check_forward_ad` are `True` (an OpInfo using this is added later in the stack).
- Tests for the gradcheck functionality
- Tests that basic out-of-place op works
Test Plan: Imported from OSS
Reviewed By: albanD, saketh-are
Differential Revision: D31842018
Pulled By: soulitzer
fbshipit-source-id: 84b18d9a77eeb19897757e37555581f2a9dc43d8
