Menu Customizer: completely hide inactive reorder buttons from assistive technologies

[afercia]

When the menu items reorder buttons are disabled, they have a tabindex="-1" attribute set to remove them from tab order. By the way screen reader users can still use arrows to read content as they normally do for any element in the page. See in the screenshot below how using arrows the disabled buttons are actually announced.

I'd propose to completely hide them using also aria-hidden="true". This way, users will get only the controls they can actually use, reducing noise and potential confusion.

[ocean90]

In 33412:

Customizer: Hide inactive reorder buttons for menu items from assistive technologies.

props afercia.
fixes #33114.