[numpy] Alias `arctan2` to `atan2` (#67010)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/65906
Adds an alias `arctan2` to improve numpy compatibility
cc mruberry rgommers
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67010
Reviewed By: anjali411
Differential Revision: D32378998
Pulled By: mruberry
fbshipit-source-id: 424c5c10c12b49c20ee83ccd109325c480b5b6cf
