[turbofan] Add toLowerCase, toUpperCase operators to the infamous escape analysis list.

test/mjsunit/compiler/regress-733181.js

+// Copyright 2017 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: --allow-natives-syntax
+
+function l(s) {
+  return ("xxxxxxxxxxxxxxxxxxxxxxx" + s).toLowerCase();
+}
+
+l("abcd");
+l("abcd");
+%OptimizeFunctionOnNextCall(l);
+l("abcd");
+
+function u(s) {
+  return ("xxxxxxxxxxxxxxxxxxxxxxx" + s).toUpperCase();
+}
+
+u("abcd");
+u("abcd");
+%OptimizeFunctionOnNextCall(u);
+u("abcd");