Add `farthest-side` to fix needs-attention badge circle

While testing my "unread-items" implementation from libhandy (libhandy!733 (closed)), I noticed that the needs-attention badge on libadwaita is pretty square:

So, this MR just adds the farthest-side argument, as seen in the GTK css, to make the badge round again:

It's also restores that one page one the ViewSwitcher Demo is set to need attention.