[JIT] Improve class type annotation inference (#46422)
**Summary**
In `try_ann_to_type`, if an annotation has an attribute named
`__torch_script_class__`, it is assumed to be a TorchScript class that
has already been scripted. However, if it is a class that extends
another class, this code path causes a crash because it looks up the
JIT type for the class by name in the compilation unit. This JIT type
obviously cannot exist because inheritance is not supported.
This commit fixes this by looking up the qualified name of a class
in torch.jit._state._script_class in order to ascertain whether it has
already been scripted (instead of looking for a `__torch_script_class__`
attribute on the class object.
**Test Plan**
This commit adds a unit test consisting of the code sample from the
issue that reported this problem.
**Fixes**
This commit fixes #45860.
ghstack-source-id: 6fe19a45c694c1f9d7fb0e77bc72bd03ef2bf160
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45940
