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/quickfix/createFromUsage/createVariable/property/afterValOnClassObject.kt

@@ -2,7 +2,7 @@
 // ERROR: Property must be initialized or be abstract
 
 class A<T>(val n: T) {
-    class object {
+    default object {
         val foo: Int
 
     }