Kotlin's implementation of defaults depends on the -Xjvm-default setting (or the @JvmDefault deprecated annotation, not implemented here): by default, actual interface class files don't use default method, and any class that would inherit one instead implements the interface calling a static method defined on TheInterface$DefaultImpls. With
-Xjvm-default=all or =all-compatibility, real interface default methods are emitted, with the latter retaining the DefaultImpls methods so that other Kotlin can use it.
Here I adopt a hybrid solution: create a real default method implementation, but also emit a forwarding method like `@override int f(int x) { return super.TheInterface.f(x); }`, because the Java extractor will see `MyClass.f` in the emitted class file and try to dispatch directly to it. The only downside is that we emit a default interface
method body for a prototype that will appear to be `abstract` to the Java extractor and which it will extract as such. I work around this by tolerating the combination `default abstract` in QL. The alternative would be to fully mimic the DefaultImpls approach, giving 100% fidelity to kotlinc's strategy and therefore no clash with the Java
extractor's view of the world.
This generates functions that omit parameters with default values, rightmost first, such that Java can achieve a similar experience to Kotlin (which represents calls internally as if the default was supplied explicitly, and/or uses a $default method that supplies the needed arguments).
A complication: combining JvmOverloads with JvmStatic means that both the companion object and the surrounding class get overloads.
Previously these would get extracted unlike other private methods even if the class was a standard library or other external class. This could cause inconsistencies because if we also compiled the class from source we could end up deciding different names for the property's setter: setXyz$private when seen from source, and setXyz without a
suffix when seen as an external .class file. Avoiding extracting these functions from the external perspective both restores consistency with other kinds of method and avoids these consistency problems.
