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/boxWithStdlib/native/nativePropertyAccessors.kt

@@ -1,5 +1,5 @@
 class C {
-    class object {
+    default object {
         val defaultGetter: Int = 1
             [native] get
 

compiler/testData/codegen/boxWithStdlib/native/privateStatic.kt

@@ -2,7 +2,7 @@ import kotlin.jvm.*
 import kotlin.platform.*
 
 class C {
-    class object {
+    default object {
         private platformStatic native fun foo()
     }
 

compiler/testData/codegen/boxWithStdlib/native/staticNative.kt

@@ -4,7 +4,7 @@ import kotlin.jvm.*
 import kotlin.platform.*
 
 class WithNative {
-    class object {
+    default object {
         platformStatic native fun bar(l: Long, s: String): Double
     }
 }