PY-17627 PY-17733 Resolve class attributes defined in @classmethods

The logic is similar to that for instance attributes. Top-level class
attributes and methods defined in the class body get the precedence,
followed by class attributes defined with assignments in @classmethods
unless the latter would resolve to the same assignments as in

cls.attr = cls.attr + 1

finally, we scan through all other class methods resolving the name
to the first definition inside one of them.

So far, I intentionally didn't expose such attributes in findClassAttribute()
or getClassAttributes() because users of these methods assume that
this API considers only attributes defined immediately in the class body.
Adding extra definitions from class methods might break these usages.

I had to update the inspection about typing.Final, because it relied
on the fact that resolve() on assignment targets on class objects can
lead only to those top-level class attributes, where type hints are normally
located, but now it can lead to assignments to a qualified attribute inside
a containing class method.

GitOrigin-RevId: 0ca5bdaa4efca127ac187e822a49df6795e1028a

python/testData/completion/classAttributeDefinedInClassMethod.after.py

@@ -0,0 +1,8 @@
+class C:
+    @classmethod
+    def first(cls):
+        cls.attr = 1
+        
+    @classmethod
+    def second(cls):
+        print(cls.attr)

python/testData/completion/classAttributeDefinedInClassMethod.py

@@ -0,0 +1,8 @@
+class C:
+    @classmethod
+    def first(cls):
+        cls.attr = 1
+        
+    @classmethod
+    def second(cls):
+        print(cls.at<caret>)