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/diagnostics/tests/regressions/kt701.kt

@@ -2,7 +2,7 @@
 fun getJavaClass<T>() : java.lang.Class<T> { return "" <!CAST_NEVER_SUCCEEDS!>as<!> Class<T> }
 
 public class Throwables() {
-    class object {
+    default object {
         public fun propagateIfInstanceOf<X : Throwable?>(throwable : Throwable?, declaredType : Class<X<!BASE_WITH_NULLABLE_UPPER_BOUND!>?<!>>?) {
             if (((throwable != null) && declaredType?.isInstance(throwable)!!))
             {