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/properties/kt1482_2279.kt

@@ -1,7 +1,7 @@
 abstract class ClassValAbstract {
     abstract var a: Int
 
-    class object {
+    default object {
         val methods = (this as java.lang.Object).getClass()?.getClassLoader()?.loadClass("ClassValAbstract")?.getMethods()!!
     }
 }