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/ClassObjectDefaultVisibility.kt

@@ -1,14 +1,14 @@
 package test
 
 public class Pub {
-    class object {}
+    default object {}
 }
 
 private class Pri {
-    class object {}
+    default object {}
 }
 
 class Int {
-    class object {}
+    default object {}
 }