Enhance item filtering capabilities on walk_nav_menu_tree

[tomtomp]

Could it be possible in "wp-includes/nav-menu-template.php" at line 104 to change :

$output .= apply_filters( 'wp_get_nav_menu_item', $item_output, $args);

for:

$output .= apply_filters( 'wp_get_nav_menu_item', $item_output, $args, $item );

so it will possible to insert information (item ID, alt, ...) trough sprintf before or after item

Thanks

(In [14600]) s/wp_get_nav_menu_item/walker_nav_menu_start_el/ to be more specific. Pass all start_el() args to the filter. Props tomtomp. fixes #13366