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/codegen/boxWithJava/properties/classObjectProperties/classObjectProperties.kt

@@ -1,17 +1,17 @@
 class Klass {
-    class object {
+    default object {
         val NAME = "Klass"
     }
 }
 
 trait Trait {
-    class object {
+    default object {
         val NAME = "Trait"
     }
 }
 
 enum class Enoom {
-    class object {
+    default object {
         val NAME = "Enoom"
     }
 }