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/bytecodeText/staticFields/classObject.kt

@@ -1,7 +1,7 @@
 class A {
-    class object {
+    default object {
         val r: Int = 1;
     }
 }
-// A and class object constructor call
+// A and default object constructor call
 // 2 ALOAD 0

compiler/testData/codegen/bytecodeText/staticFields/classObjectSyntheticAccessor.kt

@@ -1,8 +1,8 @@
 class A {
-    class object {
+    default object {
         private var r: Int = 1;
     }
 }
-// A and class object constructor call
+// A and default object constructor call
 // 2 ALOAD 0
 // 1 synthetic access\$getR