Fix backward of binary_cross_entropy_with_logits
The previous PR in this stack uncovered an error in the forward over
backward for this function.
In this PR, we fix this error and we also fix the gradgrad
implementation (and make it more stable and faster using `logsigmoid`).
We also move the double backward for this function to `FunctoinsManual`
as there's no reason for it to be in `native_functions`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/79381
Approved by: https://github.com/soulitzer
