Returns float tensors for complex inputs to abs (#35871)
Summary:
Per title. A test is added to test_type_promotion for the behavior. This behavior is consistent with NumPy's.
For complex inputs to `abs` the result is cast to float after the computation since the computation of abs must be performed on the original complex tensor. While `std::abs` returns a float value when called on complex inputs, returning a FloatTensor directly would require additional loop instantiations in TensorIterator. This may be worthwhile to pursue in the future.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35871
Differential Revision: D20961711
Pulled By: mruberry
fbshipit-source-id: 232f62cf64caa4154eb2194969efa51d2082d842
