Add fused modules in nn._intrinsic (#22999)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22999
Using nn.Sequential to represent fused modules
Reviewed By: zafartahirov
Differential Revision: D16349133
fbshipit-source-id: 04d862ac4a0d20e83dc9d6de6b7d0d0c26bdedfd
