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/class/deprecatedFlag/classObject.kt

@@ -1,5 +1,5 @@
 class MyClass {
-    deprecated("") class object {
+    deprecated("") default object {
 
     }
 }

compiler/testData/writeFlags/class/visibility/private/innerEnum.kt

@@ -1,4 +1,4 @@
-// NO_FLAGS because we put enum in class object of foo. When it will be fixed - MyClass should have ACC_PRIVATE flag
+// NO_FLAGS because we put enum in default object of foo. When it will be fixed - MyClass should have ACC_PRIVATE flag
 
 class Foo {
   private enum class MyClass() {