Left shadow in app-navigation missing from user settings

[skjnldsv]

Since we're using anchor, the active state isn't applied.
We need to change that.

• Change the active state while scrolling with the screen position
  • Screen position
  • Active state on last item too (since the window height might be too much)

OR, we switch from a single page to a multiple page like the admin settings

@nextcloud/designers

[MorrisJobke]

This is now implemented in Nextcloud 13