Add append method for nn.Sequential (#71326)
Summary:
Partially addresses https://github.com/pytorch/pytorch/issues/71249, and potentially supersedes https://github.com/pytorch/pytorch/pull/20274.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71326
Reviewed By: cpuhrsch
Differential Revision: D33855047
Pulled By: jbschlosser
fbshipit-source-id: a3a682e206f93b4c52bc3405e2f7b26aea6635ea
(cherry picked from commit c0b27bbf2a12c970abef4c64e419bfc4840aa8ea)
