Automatic no longer leaves the keyboard under the system's buttons in
gesture navigation.

It was reserving the smaller of two insets, and on a phone in gesture
navigation those two describe different things: the tappable inset is
the gesture bar's own bounding box, while the navigation bar's inset is
the whole zone the hide-keyboard and switch-keyboard buttons live in.
Taking the smaller lifted the keyboard clear of the gesture bar and left
it under the buttons.

The navigation bar is the furniture, so that is the number Automatic
uses now - still capped by how much of it is actually over the keyboard's
own window, which is what keeps it at nothing on phones that place the
keyboard above the bar already.

Reported with measurements from two phones and several navigation
settings. Thank you.
