Port `log_softmax` to structured kernel (#57374)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/57374
Test Plan: Imported from OSS
Reviewed By: saketh-are
Differential Revision: D30240243
Pulled By: SplitInfinity
fbshipit-source-id: de6617c75d16e26d607a884c25b8752b7b561737
