Pretty printing of C++ modules (#15326)
Summary:
A long outstanding nicety: pretty printing of C++ modules. E.g.
```
Sequential sequential(
Linear(10, 3),
Conv2d(1, 2, 3),
Dropout(0.5),
BatchNorm(5),
Embedding(4, 10),
LSTM(4, 5));
std::cout << sequential;
```
prints
```
torch::nn::Sequential(
(0): torch::nn::Linear(in=10, out=3, with_bias=true)
(1): torch::nn::Conv2d(input_channels=1, output_channels=2, kernel_size=[3, 3], stride=[1, 1])
(2): torch::nn::Dropout(rate=0.5)
(3): torch::nn::BatchNorm(features=5, eps=1e-05, momentum=0.1, affine=true, stateful=true)
(4): torch::nn::Embedding(count=4, dimension=10)
(5): torch::nn::LSTM(input_size=4, hidden_size=5, layers=1, dropout=0)
)
```
apaszke ebetica ezyang
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15326
Differential Revision: D13518986
Pulled By: goldsborough
fbshipit-source-id: 63bf753672f0e348951de3645208f263581de5fb
