Replace 'class object' with 'default object' in renderers and test data

Includes changes to decompiled text
Old syntax is used in builtins and project code for now

compiler/testData/loadJava/compiledKotlin/classObject/NamedClassObject.txt

@@ -3,7 +3,7 @@ package test
 internal final class NamedClassObject {
     /*primary*/ public constructor NamedClassObject()
 
-    internal class object Named {
+    internal default object Named {
         /*primary*/ private constructor Named()
         internal final fun f(): kotlin.Int
     }