[strong] Implement revised strong class semantics

test/mjsunit/strong/class-weak-extend.js

-// Copyright 2015 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Flags: --strong-mode --allow-natives-syntax
-
-function getStrongClass() {
-  "use strong";
-  return (class {});
-}
-
-function weakClass() {
-  "use strict";
-  class Weak extends getStrongClass() {}
-}
-
-function strongClass() {
-  "use strong";
-  class Strong extends getStrongClass() {}
-}
-
-assertThrows(weakClass, TypeError);
-%OptimizeFunctionOnNextCall(weakClass);
-assertThrows(weakClass, TypeError);
-
-assertDoesNotThrow(strongClass);
-%OptimizeFunctionOnNextCall(strongClass);
-assertDoesNotThrow(strongClass);