Added Encoder Layer constructor with default parameters (#43130)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/37756
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43130
Reviewed By: colesbury
Differential Revision: D23189803
Pulled By: mrshenli
fbshipit-source-id: 53f3fca838828ddd728d8b44c36745bab5acee1f
