Implement $default method synthesis

This adds methods that fill in default parameters whenever a constructor or method uses default parameter values. I use as similar an approach to the real Kotlin compiler as possible both because this produces the desirable dataflow, and because it should merge cleanly with the same class file seen by the Java extractor, which will see and
extract the signatures of the default methods.

java/ql/lib/semmle/code/java/Element.qll

@@ -65,6 +65,8 @@ class Element extends @element, Top {
       i = 8 and result = "Proxy static method for a @JvmStatic-annotated function or property"
       or
       i = 9 and result = "Forwarder for a @JvmOverloads-annotated function"
+      or
+      i = 10 and result = "Forwarder for Kotlin calls that need default arguments filling in"
     )
   }
 }