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/tests/variance/privateToThis/FunctionCall.kt

@@ -27,7 +27,7 @@ class Test<in I> {
         t.apply(t.<!INVISIBLE_MEMBER(foo; private/*private to this*/; Test)!>foo<!>())
     }
 
-    class object {
+    default object {
         fun <I> test(t: Test<I>) {
             t.apply(t.<!INVISIBLE_MEMBER(foo; private/*private to this*/; Test)!>foo<!>())
         }

compiler/testData/diagnostics/tests/variance/privateToThis/FunctionCall.txt

@@ -14,7 +14,7 @@ internal final class Test</*0*/ in I> {
     internal final fun </*0*/ I> test(/*0*/ t: Test<I>): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 
-    internal class object Default {
+    internal default object Default {
         private constructor Default()
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int

compiler/testData/diagnostics/tests/variance/privateToThis/GetVal.kt

@@ -26,7 +26,7 @@ class Test<in I, out O> {
         t.apply(t.<!INVISIBLE_MEMBER(i; private/*private to this*/; Test)!>i<!>)
     }
 
-    class object {
+    default object {
         fun <I, O> test(t: Test<I, O>) {
             t.apply(t.<!INVISIBLE_MEMBER(i; private/*private to this*/; Test)!>i<!>)
         }

compiler/testData/diagnostics/tests/variance/privateToThis/GetVal.txt

@@ -14,7 +14,7 @@ internal final class Test</*0*/ in I, /*1*/ out O> {
     internal final fun </*0*/ I, /*1*/ O> test(/*0*/ t: Test<I, O>): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 
-    internal class object Default {
+    internal default object Default {
         private constructor Default()
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int

compiler/testData/diagnostics/tests/variance/privateToThis/SetVar.kt

@@ -26,7 +26,7 @@ class Test<in I, out O> {
         t.<!INVISIBLE_MEMBER(i; private/*private to this*/; Test)!>i<!> = getT()
     }
 
-    class object {
+    default object {
         fun <I, O> test(t: Test<I, O>) {
             t.<!INVISIBLE_MEMBER(i; private/*private to this*/; Test)!>i<!> = getT()
         }

compiler/testData/diagnostics/tests/variance/privateToThis/SetVar.txt

@@ -14,7 +14,7 @@ internal final class Test</*0*/ in I, /*1*/ out O> {
     internal final fun </*0*/ I, /*1*/ O> test(/*0*/ t: Test<I, O>): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 
-    internal class object Default {
+    internal default object Default {
         private constructor Default()
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int