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/writeFlags/innerClass/visibility/publicClassObject.kt

@@ -1,5 +1,5 @@
 class Foo {
-  public class object {
+  public default object {
   }
 }