Add test for freezing of module namespace object (#3213)

Attempting to freeze the module namespace exotic object should not affect the `writable`-ity of the properties as that exercises the same `DefineOwnProperty` operation according to [`SetIntegrityLevel`](https://tc39.es/ecma262/#sec-setintegritylevel).

@erights discovered a [bug in v8](https://bugs.chromium.org/p/v8/issues/detail?id=12240) where, while the `Object.freeze` operation throws, it actually makes exported properties non-writable one by one.

At the request of @syg, I'm contributing a test against this behavior. The bug in v8 actually leads to a breakage of the objects invariants, however I'm not testing for that here as the root cause is the illegal freezing of the export.

test/language/module-code/namespace/internals/define-own-property.js

@@ -114,3 +114,24 @@ assert.throws(TypeError, function() {
       {value: "module", writable: false, enumerable: false,
        configurable: false});
 }, 'Object.defineProperty: Symbol.toStringTag');
+
+
+// Indirect change requested through Object.freeze
+
+// Try freezing more times than there are exported properties
+for (let i = 1; i < exported.length + 2; i++) {
+  assert.throws(
+    TypeError,
+    function () {
+      Object.freeze(ns);
+    },
+    "Object.freeze: " + String(i)
+  );
+}
+
+for (const key of exported) {
+  const desc = Object.getOwnPropertyDescriptor(ns, key);
+  assert.sameValue(desc.writable, true, String(key) + " writable");
+}
+
+assert(!Object.isFrozen(ns), "namespace object not frozen");