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/testsWithJsStdLib/native/nativeSetter/onNativeClassMembers.kt

@@ -17,7 +17,7 @@ class A {
     nativeSetter
     fun set5(a: Double, v: String): CharSequence = "OK"
 
-    class object {
+    default object {
         nativeSetter
         fun set(a: String, v: Any?): Any? = null
 
@@ -43,7 +43,7 @@ class B {
     nativeSetter
     <!NATIVE_ANNOTATIONS_ALLOWED_ONLY_ON_MEMBER_OR_EXTENSION_FUN!>object Obj1<!> {}
 
-    class object {
+    default object {
         <!NATIVE_ANNOTATIONS_ALLOWED_ONLY_ON_MEMBER_OR_EXTENSION_FUN!>nativeSetter
         val foo<!> = 0