Add derivative of cholesky_solve (#26185)
Summary:
Changelog:
- Add derivative of cholesky_solve. The equations are derived akin to the derivative of solve methods using the technique detailed [here](https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwiXrOjIyM7kAhWstlkKHRxqCDgQFjAAegQIAhAC&url=https%3A%2F%2Fpeople.maths.ox.ac.uk%2Fgilesm%2Ffiles%2FNA-08-01.pdf&usg=AOvVaw0BNISOvM_I9KjPrl0xv1R_)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26185
Test Plan:
- Added tests for cholesky_solve in test_autograd.py
Closes half of https://github.com/pytorch/pytorch/issues/4669.
Differential Revision: D17408123
Pulled By: soumith
fbshipit-source-id: f9668c8d4d758c0dc658941a8b730a17683091aa
