Disallow auto_element_wise for in-place and fix some in-place gradients (#85634)
Fixes https://github.com/pytorch/pytorch/issues/85535
Also fixes the backward and forward gradients of `nn.functional.threshold`. The issue was that in-place gradients weren't tested because the in-place variants were not properly registered to the OpInfo.
Perhaps an alternative to this to make auto_element_wise smart enough to actually handle the in-places cases (we have 4 cases total now where we manually copy_ after doing auto_element_wise), but that requires a few more changes.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85634
Approved by: https://github.com/albanD
