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

j2k/testData/fileOrElement/class/ClassShadowing.kt

@@ -1,7 +1,7 @@
 package test
 
 public class Short {
-    class object {
+    default object {
         public fun valueOf(value: String): Short {
             return Short()
         }
@@ -9,7 +9,7 @@ public class Short {
 }
 
 class Test {
-    class object {
+    default object {
         public fun test() {
             test.Short.valueOf("1")
             test.Short.valueOf("1")