Handle references to fields with inheritance in closures.

test/super/implicit_name.wren

@@ -0,0 +1,16 @@
+class Base {
+  foo {
+    IO.print("Base.foo")
+  }
+}
+
+class Derived is Base {
+  foo {
+    IO.print("Derived.foo")
+    super
+  }
+}
+
+(new Derived).foo
+// expect: Derived.foo
+// expect: Base.foo