iter 22-tidy.6.2: write_fn_def renders forall class constraints

examples/test_22b2_constraint_declared_via_superclass.prose.txt

@@ -0,0 +1,14 @@
+// module test_22b2_constraint_declared_via_superclass
+
+class Eq a {
+  fn eq(x: a, x1: a) -> Bool
+}
+
+class Ord a extends Eq {
+  fn lt(x: a, x1: a) -> Bool
+}
+
+forall<a> where Ord a
+fn uses_eq_via_ord(x: a, y: a) -> Bool {
+  eq(x, y)
+}