Convert contributed descriptors to list...

without this `KDocCompletionTestGenerated,testExtensionsFQLink`, which
most likely point to some broken contract in the test.

compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassMemberScope.kt

@@ -67,7 +67,7 @@ open class LazyClassMemberScope(
             )
         )
         result.addAll(computeExtraDescriptors(NoLookupLocation.FOR_ALREADY_TRACKED))
-        result
+        result.toList()
     }
 
     override fun getContributedDescriptors(