C++ API: torch::nn::Softmax2d (#27509)
Summary:
Add torch::nn::Softmax2d module support for the C++ API.
Softmax2d only supports module in Python API, so this PR adds only module support as well.
This PR is WIP because it uses the function in https://github.com/pytorch/pytorch/issues/27446 .
After https://github.com/pytorch/pytorch/issues/27446 is merged, I will remove WIP.
Related Issue: https://github.com/pytorch/pytorch/issues/25883
Reviewer: yf225
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27509
Differential Revision: D17899715
Pulled By: yf225
fbshipit-source-id: bd891bc995f5a92bf4f5405f8bf07d1bd5de2479
