add a debug api to extract cache entry from code (#106673)
Per the discussion with @jansel in https://dev-discuss.pytorch.org/t/how-are-guards-installed-on-frames-that-are-transient-objects/1415/7 , guards and compiled code live in `co_extra` field in pycodeobject, which cannot be accessed in a trivial way. This PR tries to add a debug API to extract the data from that field, which can make debugging torchdynamo much easier.
The API is intended to be used for debug only, and should have no compatibility issues with the current system.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106673
Approved by: https://github.com/jansel
