`RuntimeTypeMapper.mapSignature` threw exception because the descriptor
for `clone` was created manually in CloneableClassScope and therefore it
didn't have a JVM signature as in deserialized descriptors, and wasn't
recognized as a Java method either.
#KT-22923 Fixed
Caused by 4266e50be8 and 8ccbbf71ec. Previously it worked because we
used hardcoded signatures of equals/hashCode/toString and always looked
them up in java.lang.Object
#KT-25404 Fixed