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/property/classObject/trait/publicVarPrivateSet.kt

@@ -1,5 +1,5 @@
 trait Test {
-  class object {
+  default object {
     public var prop: Int = 0
       private set
   }