Always extract methods of user-class supertypes

This matches the Java extractor's behaviour. Also if we re-visit a class to extract its members, revisit its supertypes to extract their members too.

java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt

@@ -321,7 +321,8 @@ open class KotlinFileExtractor(
             }
 
             extractClassModifiers(c, id)
-            extractClassSupertypes(c, id)
+            val forceExtractSupertypeMembers = !isExternalDeclaration(c)
+            extractClassSupertypes(c, id, inReceiverContext = forceExtractSupertypeMembers)
 
             return id
         }