Adjust to any display size
Adjust the keyboard shape and size so that it works on narrow displays, but also tries to avoid occupying the entire screen if the display is wide, and remains finger-pushable.
It should work on degenerate displays (<1:3 proportions).
- assume a finger size and adjust based on the output dimensions
- guess finger size from the output use case (tablet, phone, table), as in https://phabricator.kde.org/T10462
- leave empty space on the side(s)
- have dedicated layouts for weird proportions