[JIT] Tweak annotation extraction for py3.10 (#81334)
The way Python-3.10+ deals with annotations has changed, see
https://docs.python.org/3/howto/annotations.html#accessing-the-annotations-dict-of-an-object-in-python-3-10-and-newer
In particular, derived classes would not inherit parent annotations as
following example clearly demonstrates:
```
class Base:
a: int = 3
b: str = 'abc'
class Derived(Base):
pass
print(Derived.__annotations__)
```
if executed by 3.10 runtime, it will return an empty dict, while older
ones return annotations of the base class
Fix that by implementing this difference in `get_annotations` function
I wonder if in general, we should do it even for older versions of Python runtime
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81334
Approved by: https://github.com/suo
