keyboard: Request a bigger size in portrait orientation
In portrait orientation, we set the height to the preferred height for the monitor width (or, if smaller, a third o the screen height).
However as the forWidth currently doesn't make a difference, the height is effectively controlled by the natural height of the keys - which is rather small.
Address this by making AspectContainer request an appropriate preferred size based on the fixed ratio.
Fixes #2349 (closed)