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/redeclarations/PropertyAndInnerClass.kt

@@ -5,7 +5,7 @@ public class A() {
 }
 
 public class B() {
-   class object {
+   default object {
       public val <!REDECLARATION!>FOO<!>: String = "test"
       
       public class <!REDECLARATION!>FOO<!>() { }