intl: increase coverage for NumberFormat constructor

Increase coverage for the Intl.NumberFormat class contructor by adding
tests for checking that it calls ToObject on the locales argument.

test/intl402/NumberFormat/constructor-locales-tooptions.js

+// Copyright (C) 2018 Ujjwal Sharma. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-initializenumberformat
+description: >
+  Tests that Intl.NumberFormat contructor converts the locales argument
+  to an object using `ToObject` (7.1.13).
+info: |
+  9.2.1 CanonicalizeLocaleList
+
+  4.a. Let O be ? ToObject(locales).
+---*/
+
+const toObjectResults = [[true, new Boolean(true)], [42, new Number(42)]];
+
+// Test if ToObject is used to convert primitives to Objects.
+toObjectResults.forEach(pair => {
+  const [value, result] = pair;
+  assert.sameValue(
+    new Intl.NumberFormat(value).resolvedOptions(),
+    new Intl.NumberFormat(result).resolvedOptions()
+  );
+});
+
+// ToObject throws a TypeError for undefined and null, but it's not called
+// when locales is undefined.
+assert.throws(TypeError, () => new Intl.NumberFormat(null));