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/diagnostics/tests/classObjects/resolveFunctionInsideClassObject.kt

@@ -3,7 +3,7 @@ package test
 class Test {
   fun test(): Int = 12
 
-  class object {
+  default object {
     val a = <!INACCESSIBLE_OUTER_CLASS_EXPRESSION!>test()<!> // Check if resolver will be able to infer type of a variable
   }
 }