Add C++ API clip_grad_value_ for nn:utils (#28736)
Summary:
Adds C++ API clip_grad_value_ for torch::nn:utils module.
Also, fix the for indent level error in the original test/test_nn.py.
Issue: https://github.com/pytorch/pytorch/issues/25883
Reviewer: yf225
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28736
Differential Revision: D18263807
Pulled By: yf225
fbshipit-source-id: 29282450bd2099df16925e1d0edd3d933f6eeb9b
