[refactor] Adding FoldConvBatchNorm2dHelper (#32374)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32374
Moving all fold conv bn code to a class to prepare for making
it work with shared ClassType
Test Plan:
compiles
Imported from OSS
Differential Revision: D19508032
fbshipit-source-id: 4e9cf714111305d2b5474d4506507078f69f0c84
