Outside of tablet mode, you don't need a virtual keyboard except for the
extremely niche case of not having a physical keyboard plugged into a
desktop machine. For all other use cases, the tray item to show and
hide the virtual keyboard is an annoyance when you're not in tablet
mode, so let's demote it to the expanded popup to save space in the
System Tray and make its contents more contextually relevant.
It's mostly useful to be able to hide the virtual keyboard like we do in
Plasma Mobile from the bottom panel, should probably replace the SNI
from KWin.