[dynamo][guards-c++-refactor] Introduce LeafGuard, GuardManager and GuardAccessor classes (#119822)
The full blown implementation is in this stack - https://github.com/pytorch/pytorch/pull/110590 which is passing all the test cases on CI. That stack is hard to review. So, breaking apart.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/119822
Approved by: https://github.com/jansel
