Add ClassDescriptorFactory#getAllContributedClassesIfPossible

Currently a no-op, will be used soon to make Cloneable a synthesized class,
visible in scope's getContributedDescriptors()

core/descriptors/src/org/jetbrains/kotlin/builtins/functions/BuiltInFictitiousFunctionClassFactory.kt

@@ -83,4 +83,10 @@ class BuiltInFictitiousFunctionClassFactory(
 
         return FunctionClassDescriptor(storageManager, containingPackageFragment, kind, arity)
     }
+
+    override fun getAllContributedClassesIfPossible(packageFqName: FqName): Collection<ClassDescriptor> {
+        // We don't want to return 256 classes here since it would cause them to appear in every import list of every file
+        // and likely slow down compilation very much
+        return emptySet()
+    }
 }

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/ClassDescriptorFactory.kt

@@ -25,4 +25,7 @@ interface ClassDescriptorFactory {
     fun shouldCreateClass(packageFqName: FqName, name: Name): Boolean
 
     fun createClass(classId: ClassId): ClassDescriptor?
+
+    // Note: do not rely on this function to return _all_ classes. Some factories can not enumerate all classes that they're able to create
+    fun getAllContributedClassesIfPossible(packageFqName: FqName): Collection<ClassDescriptor>
 }

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/descriptors/DeserializedPackageMemberScope.kt

@@ -42,7 +42,8 @@ open class DeserializedPackageMemberScope(
     private val packageFqName = packageDescriptor.fqName
 
     override fun getContributedDescriptors(kindFilter: DescriptorKindFilter, nameFilter: (Name) -> Boolean)
-            = computeDescriptors(kindFilter, nameFilter, NoLookupLocation.WHEN_GET_ALL_DESCRIPTORS)
+            = computeDescriptors(kindFilter, nameFilter, NoLookupLocation.WHEN_GET_ALL_DESCRIPTORS) +
+              c.components.fictitiousClassDescriptorFactories.flatMap { it.getAllContributedClassesIfPossible(packageFqName) }
 
     override fun hasClass(name: Name) =
             super.hasClass(name) || c.components.fictitiousClassDescriptorFactories.any { it.shouldCreateClass(packageFqName, name) }