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/codegen/box/classes/kt1018.kt

@@ -4,7 +4,7 @@ public class StockMarketTableModel() {
         return COLUMN_TITLES?.size()!!
     }
 
-    class object {
+    default object {
         private val COLUMN_TITLES : Array<Int?> = arrayOfNulls<Int>(10)
     }
 }