Port convtranspose2d (#20994)
Summary:
this PR will resolve partially https://github.com/pytorch/pytorch/issues/18353
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20994
Differential Revision: D15876052
Pulled By: ezyang
fbshipit-source-id: 5896e0cbb656d0530e39fd681808adc685841b37
