Port replication_pad2d and replication_pad3d to ATen (#15538)
Summary:
port replication padding 2D and 3D from legacy TH API implementation
to ATen implementation.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15538
Differential Revision: D13547567
Pulled By: lhuang04
fbshipit-source-id: decfe100d9edfdcfb62f39ee23f37b6cae0d461f
