Test cases

OSK shows up when you click/tap text inputs and/or terminal window
OSK can type lowercase chars
Tapping "Shift" switches OSK to uppercase layer
OSK can type uppercase chars
After typing an uppercase char, OSK switches back to lowercase layer
Once switched to Numbers layer, it stays latched until user switches to another layer
Long-pressing characters like "1" shows a popup with additional chars, typing those chars works
Tapping "Ctrl", "Alt", "Super", "Shift" adds highlight to those buttons
"Ctrl", "Alt" and/or "Super" remain latched when "Shift" is toggled on/off
Key combinations like "Ctrl + C", "Ctrl + X", "Ctrl + V", "Ctrl + A", "Ctrl + Z", "Ctrl + Shift + Z", "Ctrl + Shift + V" (in terminal), "Alt + Tab", "Super + A" work as expected
Esc, F1-12, Backspace keys work as expected
OSK doesn't switch to us-extended layout in terminal
OSK works in Gnome password modal
OSK works on lock screen screensaver
OSK works on login screen if installed as a system-wide extension
OSK settings for landscape/portrait height work

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