OSK: Eliminate wasted space and improve ergonomics

This is the current OSK:

Compared to the Windows 10 OSK on the same device: or even the AOSP keyboard (through Waydroid, on the same device again):

It looks quite strange, and the buttons are quite hard to reach with thumbs while holding a 10" tablet. It used to be somewhat bearable, but with the introduction of the suggestions bar it just became too small to use comfortably. I actually thought that empty space at the top was extra padding until I started working on these changes, when I discovered it was actually a suggestions bar for use with ibus typing booster.

Changes made in this MR make the keyboard expand to fill all empty space, and make the suggestions bar disappear when empty to save space. The keyboard is now sized independently of the suggestions bar to maintain a stable size, always filling the bottom third of the screen.

Screencast_from_06-01-2022_03_46_16_PM

A comparison using typetest.io shows an approximate 1.5x increase in typing speed: osk:

Since the keyboard can stretch now, it can also fill the bottom third of the screen in portrait mode.

I actually made it fill up to half the screen like the Windows and Android keyboards shown above at first, but then I noticed that it covered the password field in the login screen so I had to revert it.