Backend: If kotlin class extends kotlin.collection.List
write it as it's super interface (light class mode only)
IDE: Provide wrapper classes to java resolve
that try to emulate backend behaviour
For example if kotlin class implements kotlin.collections.Map,
we provide a superinterface that has abstract 'getEntries' method
and 'entrySet' method that is considered default.
In reality all those methods are generated in the class itself.
In IDE supporting this case without hacks is not feasible performance-wise
since kotlin.collection.* may not be an immediate supertype and we need
to compute all supertypes just to calculate own methods of the class
Class APIs from java point of view stays the same so we can avoid generating those methods
Otherwise we have to calculate all supertypes when getMethods() is called,
which imposes severe performance penalties
We have to pretend these methods are not 'abstract' (also we consider them 'default' for safety)
so java highlighting does not report "class should be abstract" for all inheritors
We have to manually report "class should be abstract" on some of the java inheritors,
specifically those that are implementing interfaces directly
as opposed to extending kotlin classes implementing those interfaces
This is not accurate, there are some cases when we will generate DefaultImpls class that are not covered:
- Inherited default implementations
- Annotated members
In these cases IDE will report an error when in fact code compiles
What is critical though is to be able to decide whether to build DefaultImpls light classes solely based on psi without triggering stubs calculation
- light classes: do not generate light class for package facade
- drop package facades as multifile classes compilation mode support
- get rid of some additional package facade fqName usages
- update tests for light classes
