Consider class inheriting abc.ABC as abstract (PY-30789)

python/testData/inspections/PyAbstractClassInspection/HiddenForAbstractSubclassWithABCSuperclass/a.py

@@ -0,0 +1,9 @@
+import abc
+
+class A1(abc.ABC):
+    @abc.abstractmethod
+    def m1(self):
+        pass
+
+class A2(A1, abc.ABC):
+    pass

python/testData/inspections/PyAbstractClassInspection/HiddenForAbstractSubclassWithABCSuperclass/abc.py

@@ -0,0 +1,13 @@
+class ABCMeta:
+    pass
+
+
+class ABC(metaclass=ABCMeta):
+    """Helper class that provides a standard way to create an ABC using
+    inheritance.
+    """
+    pass
+
+
+def abstractmethod(foo):
+    pass