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/boxWithJava/platformStatic/annotations/simpleClassObject.kt

@@ -7,7 +7,7 @@ annotation class testAnnotation
 
 class A {
 
-    class object {
+    default object {
         val b: String = "OK"
 
         platformStatic testAnnotation fun test1() = b