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

idea/testData/diagnosticMessage/nestedClassAcessedViaInstanceReference.kt

@@ -3,7 +3,7 @@
 
 class A {
     class Nested()
-    class NestedWithClassObject { class object }
+    class NestedWithClassObject { default object }
     enum class NestedEnum { A }
     object NestedObj { fun invoke() = 1 }
 }

idea/testData/diagnosticMessage/nestedClassAcessedViaInstanceReference2.txt

@@ -1,2 +1,2 @@
 <!-- nestedClassAcessedViaInstanceReference2 -->
-Nested class object 'Default' accessed via instance reference
+Nested default object 'Default' accessed via instance reference

idea/testData/diagnosticMessage/nestedClassShouldBeQualified.kt

@@ -15,7 +15,7 @@ fun A.B.test() {
 }
 
 class C {
-    class object {
+    default object {
         class D {
             class Nested
         }
@@ -29,7 +29,7 @@ fun C.Default.D.text() {
 
 class E {
     class F {
-        class object
+        default object
     }
 }
 

idea/testData/diagnosticMessage/nestedClassShouldBeQualified5.txt

@@ -1,2 +1,2 @@
 <!-- nestedClassShouldBeQualified5 -->
-Nested class object 'Default' should be qualified as 'E.F.Default'
+Nested default object 'Default' should be qualified as 'E.F.Default'