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/loadJava/compiledKotlin/classObject/ClassObjectExtendsTrait.kt

@@ -3,6 +3,6 @@ package test
 trait Bbb
 
 class ClassObjectextendsTrait {
-    class object : Bbb {
+    default object : Bbb {
     }
 }