Add descriptor tests for sec-array.isarray

test/built-ins/Array/isArray/Array.isArray-descriptor.js

+// Copyright 2017 Lyza Danger Gardner. All rights reserved.
+// This code is governed by the license found in the LICENSE file.
+
+/*---
+description: Testing descriptor property of Array.isArray
+includes:
+    - propertyHelper.js
+esid: sec-array.isarray
+---*/
+
+verifyWritable(Array, "isArray");
+verifyNotEnumerable(Array, "isArray");
+verifyConfigurable(Array, "isArray");