Expose test utils (#20114)
Summary:
Some functions were not decorated with `CAFFE2_API`, makes them unusable when creating unit tests for custom ops outside Caffe2 repo.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20114
Differential Revision: D15217490
Pulled By: ezyang
fbshipit-source-id: dda3910ad24e566567607deaac705a34ec8e7b8d
