default -> companion: replace all mentions of default and default object

compiler/testData/diagnostics/tests/MultipleBounds.kt

@@ -17,7 +17,7 @@ trait G<X> {
 class C() : A(), B
 
 class D() {
-  default object : A(), B {}
+  companion object : A(), B {}
 }
 
 class Test1<T : A>()
@@ -72,7 +72,7 @@ val t3 = test2<C>(C())
 
 class Test<T>
   where
-    <!UNSUPPORTED!>class object T : <!FINAL_DEFAULT_OBJECT_UPPER_BOUND!>Foo<!><!>,
+    <!UNSUPPORTED!>class object T : <!FINAL_COMPANION_OBJECT_UPPER_BOUND!>Foo<!><!>,
     <!UNSUPPORTED!>class object T : A<!> {}
 
 val <T, B : T> x : Int = 0