avg_pool2d: port to structured (#58987)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/58987
Test Plan: Imported from OSS
Reviewed By: anjali411
Differential Revision: D28717067
Pulled By: ezyang
fbshipit-source-id: 984a8ae8bc05811b787fdac565566f359b55a3d6
