stft: Require return_complex to be passed explicitly for real input (#86724)
This behavior has been deprecated since PyTorch 1.8 but this step of
the deprecation cycle was put on hold in #50102 waiting for JIT
upgraders functionality which doesn't seem to have panned out. I'd say
there has been more than enough of a deprecation period, so we should
just continue.
BC-breaking message:
`torch.stft` takes an optional `return_complex` parameter that
indicates whether the output should be a floating point tensor or a
complex tensor. `return_complex` previously defaulted to `False` for
real input tensors. This PR removes the default and makes
`return_complex` a required argument for real inputs. However, complex
inputs will continue to default to `return_complex=True`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86724
Approved by: https://github.com/mruberry, https://github.com/albanD
