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/box/delegatedProperty/kt4138.kt

@@ -5,14 +5,14 @@ class Delegate<T>(var inner: T) {
 
 
 class Foo (val f: Int) {
-    class object {
+    default object {
         val A: Foo by Delegate(Foo(11))
         var B: Foo by Delegate(Foo(11))
     }
 }
 
 trait FooTrait {
-    class object {
+    default object {
         val A: Foo by Delegate(Foo(11))
         var B: Foo by Delegate(Foo(11))
     }

compiler/testData/codegen/box/delegatedProperty/propertyMetadataShouldBeCached.kt

@@ -3,7 +3,7 @@ import java.util.IdentityHashMap
 class A {
     var foo: Int by IntHandler
 
-    class object {
+    default object {
         var bar: Any? by AnyHandler
     }
 }