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/ClassObjects.kt

@@ -4,7 +4,7 @@ class A {
   <!REDECLARATION!>class object<!> {
     val x = 1
   }
-  <!MANY_CLASS_OBJECTS, REDECLARATION!>class object<!> {
+  <!MANY_DEFAULT_OBJECTS, REDECLARATION!>class object<!> {
     val x = 1
   }
 }
@@ -13,10 +13,10 @@ class AA {
   class object {
     val x = 1
   }
-  <!MANY_CLASS_OBJECTS!>class object A<!> {
+  <!MANY_DEFAULT_OBJECTS!>class object A<!> {
     val x = 1
   }
-    <!MANY_CLASS_OBJECTS!>class object AA<!> {
+    <!MANY_DEFAULT_OBJECTS!>class object AA<!> {
     val x = 1
   }
 }
@@ -26,7 +26,7 @@ class B() {
 }
 
 object b {
-  <!CLASS_OBJECT_NOT_ALLOWED!>class object<!> {
+  <!DEFAULT_OBJECT_NOT_ALLOWED!>class object<!> {
     val x = 1
   } // error
 }
@@ -35,7 +35,7 @@ val a = A.x
 val c = B.<!UNRESOLVED_REFERENCE!>x<!>
 val d = b.<!UNRESOLVED_REFERENCE!>x<!>
 
-val s = <!NO_CLASS_OBJECT!>System<!>  // error
+val s = <!NO_DEFAULT_OBJECT!>System<!>  // error
 fun test() {
   System.out.println()
   java.lang.System.out.println()

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

@@ -28,7 +28,7 @@ object O {
 fun f() {
     A.c
     A.hashCode()
-    A().<!NO_CLASS_OBJECT, NESTED_CLASS_ACCESSED_VIA_INSTANCE_REFERENCE!>Nested<!>
+    A().<!NO_DEFAULT_OBJECT, NESTED_CLASS_ACCESSED_VIA_INSTANCE_REFERENCE!>Nested<!>
     A.Nested()
     A().Inner()
     A.Default.<!UNRESOLVED_REFERENCE!>Nested<!>

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 { }
     }
-}
+}

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

@@ -1,9 +1,9 @@
 fun test() {
     class A {
-        <!CLASS_OBJECT_NOT_ALLOWED!>class object<!> {}
+        <!DEFAULT_OBJECT_NOT_ALLOWED!>class object<!> {}
     }
 
     object {
-        <!CLASS_OBJECT_NOT_ALLOWED!>class object<!> {}
+        <!DEFAULT_OBJECT_NOT_ALLOWED!>class object<!> {}
     }
 }