linalg.eig backwards and linalg.eigvals (#57276)
Summary:
This PR adds backwards support for `eig` and `eigvals`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57276
Reviewed By: ngimel
Differential Revision: D28405056
Pulled By: mruberry
fbshipit-source-id: 27ef03f139f44d75f4d319b0f3e77e99eea9bb01
