Make autograd codegen for differentiable outputs safer to use (#65823)
Summary:
This PR adds raising an error when `len(output_differentiability) != len(outputs)`
Notes in derivatives.yml tell that
> 'output_differentiability' and value a list of the same length as the number of outputs from the forward function.
but it was not enforced in codegen leading to confusion and unexpected bugs https://github.com/pytorch/pytorch/issues/65061#issuecomment-930271126.
cc ezyang albanD zou3519 gqchen pearu nikitaved soulitzer Lezcano Varal7
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65823
Reviewed By: mrshenli
Differential Revision: D31307312
Pulled By: albanD
fbshipit-source-id: caeb949e9249310dffd237e77871e6d0d784e298
