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/inference/regressions/kt702.kt

@@ -5,7 +5,7 @@ package a
 fun getJavaClass<T>() : java.lang.Class<T> { <!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>
 
 public class Throwables() {
-    class object {
+    default object {
         public fun propagateIfInstanceOf<X : Throwable?>(throwable : Throwable?, declaredType : Class<X<!BASE_WITH_NULLABLE_UPPER_BOUND!>?<!>>?) : Unit {
             if (((throwable != null) && declaredType?.isInstance(throwable)!!))
             {

compiler/testData/diagnostics/tests/inference/regressions/kt702.txt

@@ -9,7 +9,7 @@ package a {
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
         public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 
-        public class object Default {
+        public default object Default {
             private constructor Default()
             public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
             public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int