Make top-level main navigation items not clickable when there's no link associated with them

[trubach]

Currently, if you make a top-level menu item that shows up in the main navigation menu but put in no link using <nolink>, that item will appear to be a valid link, and if you click on it, it will take you back to the current page. This behavior is confusing to the user.

What we're proposing should happen instead is that if the top-level main navigation item is set to <nolink> then that item should show the sub-menu on hover, but the item itself isn't clickable and doesn't show the pointer icon.

[github-actions]

Branch bugfix/trubach/issue-944-make-top-level-main-navigation-items-not-clickable-when-there-s-no-link-associated-with-them created!