Adding MSELoss, KLDivLoss and BCELoss to C++ front-end (#27156)
Summary:
This PR adds ```MSELoss```, ```KLDivLoss``` and ```BCELoss```. The tests for ```BCELoss``` fail with the following error:
```
unknown file: Failure
C++ exception with description "autograd_meta() INTERNAL ASSERT FAILED at /home/shahriar/Contrib/pytorch/c10/core/TensorImpl.h:533, please report a bug to PyTorch. set_requires_grad is not implemented for Tensor (set_requires_grad at /home/shahriar/Contrib/pytorch/c10/core/TensorImpl.h:533)
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27156
Differential Revision: D17960323
Pulled By: yf225
fbshipit-source-id: 84b8431064f2f573679c03a8d7994e3e2f81a4d1
