Previously because extractClassInstance didn't use the declaration stack, we wouldn't notice that it was legal to refer to its type variable in the context of extracting a specialised method <-> method source-decl edge. This led to erasing the types of the source-decl, so that e.g. Map.put(...) would have signature (Object, Object) not (K, V)
as it should.
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.
