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/InnerClassInClassObject.kt

@@ -2,7 +2,7 @@
 package test
 
 class TestFirst {
-  class object {
+  default object {
     fun testing(a: InnerClass) = 45
     fun testing(a: NotInnerClass) = 45
   }