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/psi/examples/PolymorphicClassObjects.kt

@@ -9,7 +9,7 @@ open class Buildable {
 
 class List<T> {
 
-  class object : Buildable {
+  default object : Buildable {
     override fun newBuilder<E, R>() : Builder<E, R>
 
   }

compiler/testData/psi/examples/PolymorphicClassObjects.txt

@@ -132,7 +132,8 @@ JetFile: PolymorphicClassObjects.kt
       PsiElement(LBRACE)('{')
       PsiWhiteSpace('\n\n  ')
       OBJECT_DECLARATION
-        PsiElement(class)('class')
+        MODIFIER_LIST
+          PsiElement(default)('default')
         PsiWhiteSpace(' ')
         PsiElement(object)('object')
         PsiWhiteSpace(' ')

compiler/testData/psi/examples/UpdateOperation.kt

@@ -1,5 +1,5 @@
 class Pair(x : Int, y : Int) {
-  class object {
+  default object {
     fun copy(from : Pair, x : Int = from.x, y : Int = from.y) = Pair(x, y)
   }
 }

compiler/testData/psi/examples/UpdateOperation.txt

@@ -33,7 +33,8 @@ JetFile: UpdateOperation.kt
       PsiElement(LBRACE)('{')
       PsiWhiteSpace('\n  ')
       OBJECT_DECLARATION
-        PsiElement(class)('class')
+        MODIFIER_LIST
+          PsiElement(default)('default')
         PsiWhiteSpace(' ')
         PsiElement(object)('object')
         PsiWhiteSpace(' ')