Add current_item_parent-like class to the new menu framework

[rfiser]

Currently, the new menu system does not add classes like current_page_parent and current_page_ancestor to particular menu items so that it is impossible to style for example the top level item differently.

Maybe this is due to the fact that a specific page (post, category, ...) can be placed in a single menu on more positions, so that it has more top-level parents. Nonetheless, I would still like to have the "parent" classes in the menu.

If I am in the second level (or higher) in the menu structure, I need to identify the parent item and the top-level item by a class to be able to reach it by CSS.so that it is impossible to style differently the top level item

[duck_]

See #12812