We try to make the OSK 1/3rd as big as the monitor. On landscape
layouts we usually get away with it as there's plenty of horizontal
space to enlarge the OSK while keeping the OSK aspect ratio.
In portrait layout, the horizontal space is a lot more scarce so
it means we'll still have plenty of space after making the OSK as
wide as it can possibly be, which will look as odd blank space in
the OSK panel.
In order to fix this, let the OSK panel height be less than 1/3rd
the monitor size if we are dealing with portrait layouts.
Closes: https://gitlab.gnome.org/GNOME/gnome-shell/issues/2132
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