Add strong Wolfe line search for lbfgs (#8824)
Summary:
This pull request adds a line search for lbfgs. "strong Wolfe" is the default line search method in [minFunc](https://www.cs.ubc.ca/~schmidtm/Software/minFunc.html) and it is also recommended in the [Numerical Optimization](https://www.springer.com/gp/book/9780387303031) book.
The implementation is based on four sources:
+ https://www.cs.ubc.ca/~schmidtm/Software/minFunc.html
+ https://www.springer.com/gp/book/9780387303031 Algorithms 3.5, 3.6, formula 3.59
+ https://github.com/torch/optim/blob/master/lswolfe.lua
+ https://github.com/torch/optim/blob/master/polyinterp.lua
The 'lua' version is based on an old version of `minFunc`, which has been updated in 2012. I made a couple of small changes based on the updated version. Due to that, the test of comparing with `.lua` version is not consistent (that's is the reason I changed a learning rate in the test).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/8824
Differential Revision: D15783067
Pulled By: vincentqb
fbshipit-source-id: 5316d9088233981120376d79c7869d5f97e51b69
