Learn2 menu doesn't automatically scroll when paging to next item that is off-screen

Steps to reproduce in https://learn.getgrav.org:

1. Select the "Web Servers and Hosting" menu item. This is a good menu item to start on because it has a lot of sub-menu items
2. Click the right arrow. This causes the next menu item to be selected and the corresponding page to load.
3. Keep repeating step 2. Eventually, the bottom of the visible browser window is reached.
4. Repeat step 2 a few more times. The selected menu item is out of view.

If the selected menu item is off-screen, I think the menu should automatically scroll to bring it into view.

Reproduce the paging behavior at https://learn.getgrav.org using the "Web Servers and Hosting" menu item, then inspect the Learn2 theme's menu implementation to find where the selected item changes. The work is done when paging to an off-screen item automatically scrolls the menu so that item is visible.

Written by the indexing model from the issue text.