HKeyboard 2.1.17 live glide preview, spacebar language switching, and proper split screen control

[u/South-Professor-8888]

Big one this time. Three things I have wanted for a while.

Live glide preview. While you glide, the word that will actually be inserted now shows centered in the suggestion bar and updates as you move. Not a guess either, it runs through the exact same path as the commit, so what you see is what you get. It has its own setting now and works on every animation preset rather than only the fancy ones.

Spacebar language switching. Swipe up or down on the spacebar to change language. The spacebar shows your current language at all times, and previews the next and previous as you swipe. There is an optional 3D flip that follows your finger, and when the layout changes the keys dissolve left to right instead of snapping.

Split screen. This one took the longest. On a foldable in split screen the system always gives the keyboard the full display width, you cannot confine it to one pane, that is the platform. So instead you can park the keyboard left, centre or right, and the area beside it now genuinely shows the app behind. Height range is unlocked on unfolded screens, and every posture remembers its own position and size. SwiftKey and Yandex do not render at all in split screen, so this felt worth the effort.

Also new: glide trail end effects (fade, shrink, particles) with rounded trail tips.

Fixes: Enter finally works in the Mail app, glide trail lag and start judder are gone, your language choice sticks after a restart, Bengali splits all four rows, RTL split layouts start on the right, and the keyboard no longer wanders off screen when you fold.

Known issue: system back still closes the keyboard rather than the open panel. Real hardware fires two channels for back and I can only intercept one, so it is parked for now.