[JIT] Update freezing api (#52337)
Summary:
Update freezing api for 1.8, and add a corresponding C++ API. The `optimize` flag hasn't been publicly released yet, so we are able to change it without breaking BC. I will submit a PR to branch release as well, there are a few more days to do that
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52337
Reviewed By: ejguan
Differential Revision: D26491833
Pulled By: eellison
fbshipit-source-id: 6dcd74eb8f76db64ac53183d03dabdd0f101f4b5
