Add test for [[Description]] from Symbol.for (#2970)

* Add test for [[Description]] from `Symbol.for`

* fixup! Add test for [[Description]] from `Symbol.for`

Author: jugglinmike

test/built-ins/Symbol/for/description.js

@@ -0,0 +1,18 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-symbol.for
+description: Assigns the string value to the [[Description]] slot
+info: |
+    1. Let stringKey be ? ToString(key).
+    [...]
+    4. Let newSymbol be a new unique Symbol value whose [[Description]] value
+       is stringKey.
+    [...]
+    6. Return newSymbol.
+features: [Symbol, Symbol.prototype.description]
+---*/
+
+var symbol = Symbol.for({toString: function() { return 'test262'; }});
+
+assert.sameValue(symbol.description, 'test262');