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

idea/testData/diagnosticMessage/nestedClassAcessedViaInstanceReference.kt

@@ -3,7 +3,7 @@
 
 class A {
     class Nested()
-    class NestedWithClassObject { class object }
+    class NestedWithClassObject { default object }
     enum class NestedEnum { A }
     object NestedObj { fun invoke() = 1 }
 }