tests: Add test for hash of user defined class.

tests/basics/builtin_hash.py

@@ -0,0 +1,10 @@
+# test builtin hash function
+
+class A:
+    def __hash__(self):
+        return 123
+    def __repr__(self):
+        return "a instance"
+
+print(hash(A()))
+print({A():1})