Make it a proper test

Author: odersky

tests/pos/i14083.scala

@@ -0,0 +1,9 @@
+class Outer {
+  class Inner
+}
+@main def Test =
+  assert(
+    classOf[Outer#Inner]
+      .getDeclaredFields
+      .filter(_.getName == "$outer")
+      .exists(_.isSynthetic))