C++ make torch::nn::Sequential push_back(AnyModule) methods public (#34208)
Summary:
Issue https://github.com/pytorch/pytorch/issues/33192
Moves Sequential::push_back methods with AnyModule from private -> public
Allows adding an existing AnyModule via something like:
```
torch::nn::Sequential q;
auto a=torch::nn::AnyModule(torch::nn::Linear(1,2));
q->push_back(a);
q->push_back("fc",a);
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34208
Differential Revision: D20300278
Pulled By: yf225
fbshipit-source-id: 4525319bb7fb6667e43a006c9f446a2193781005
