Add visit_overloaded() to TypeQuery

Part of #730

Author: JamesGuthrie

mypy/types.py

@@ -831,6 +831,9 @@ def visit_star_type(self, t: StarType) -> bool:
     def visit_union_type(self, t: UnionType) -> bool:
         return self.query_types(t.items)
 
+    def visit_overloaded(self, t: Overloaded) -> bool:
+        return self.query_types(cast(List[Type], t.items()))
+
     def query_types(self, types: List[Type]) -> bool:
         """Perform a query for a list of types.