Rename IsDontDelete to IsConfigurable (and invert conditions)

src/elements.cc

Index: src/elements.cc
diff --git a/src/elements.cc b/src/elements.cc
index c95ca5da055cc29b104414792e37ae7fbf61b420..76b9b03bf62d51a0ff4a59127f809f8f441fef84 100644
--- a/src/elements.cc
+++ b/src/elements.cc
@@ -1364,7 +1364,7 @@ class DictionaryElementsAccessor
           uint32_t number = static_cast<uint32_t>(key->Number());
           if (new_length <= number && number < old_length) {
             PropertyDetails details = dict->DetailsAt(i);
-            if (details.IsDontDelete()) new_length = number + 1;
+            if (!details.IsConfigurable()) new_length = number + 1;
           }
         }
       }