New implementation of test/swing/regtesthelpers/Util.getSystemMnemonicKeyCodes is not correct.

It combines key codes and key masks:

    public static ArrayList<Integer> getSystemMnemonicKeyCodes() {
        String osName = System.getProperty("os.name");
        ArrayList<Integer> result = new ArrayList<>();
        if (osName.contains("OS X")) {
            result.add(KeyEvent.VK_CONTROL);
        }
        result.add(KeyEvent.ALT_MASK);
        return result;
    }

KeyEvent.VK_CONTROL and KeyEvent.ALT_MASK are combined, and then interpreted as key codes by hitMnemonics but KeyEvent.ALT_MASK is not a key code. Therefore tests which use Util.hitMnemonics fail now, for example test javax/swing/JFileChooser/8002077/bug8002077.java.