Add some admin bar methods to the printing functions

Passing unescaped data to the title property of WP_Admin_Bar::add_menu() is unsafe, because it's not escaped on output in the menu. Example:

add_action( 'admin_bar_menu', function( WP_Admin_Bar $wp_admin_bar ) {

    $title = 'Hello world<script>alert(document.cookie);</script>';
    $wp_admin_bar->add_menu( array(
        'id'    => 'wpcs-test',
        'title' => $title,
        'href'  => '#',
    ) );

} );

It would be nice if the following could be added as printing functions, so they trigger a warning when unescaped data is passed to them:

• $wp_admin_bar->add_menu
• $wp_admin_bar->add_node

I tried adding these to the WordPress_Sniff::$printingFunctions property array, but it didn't work, so this might not even be possible. The use of a specific variable name is weird, but it's a common one to use for the parameter passed to callback functions hooked onto the admin_bar_menu hook.

Any ideas about how this could be achieved?

Start by examining WordPress_Sniff::$printingFunctions and the admin_bar_menu hook usage described in the issue. Investigate how add_menu and add_node could trigger warnings for unescaped title data; done means the relevant calls are recognized and covered by the sniff's warning behavior.