Refactor: process mentions of class object

Rename usages that refer to "default object" concept now
Test data file names are left as is

compiler/testData/diagnostics/tests/classObjects/InnerClassClassObject.kt

@@ -2,7 +2,7 @@
 
 class A {
     inner class B {
-        <!CLASS_OBJECT_NOT_ALLOWED!>class object<!> { }
+        <!DEFAULT_OBJECT_NOT_ALLOWED!>class object<!> { }
     }
 }
 
@@ -22,4 +22,4 @@ class C {
     class D {
         class object { }
     }
-}
+}