Patch: Toggle text prediction

This patch adds a toggle button left of the clipboard.

Clicking the button enables or disables text prediction. The default state is restored when the keyboard is closed. It can also be reset manually by pressing and holding the switch, just as you would clear the clipboard.

While developing the patch, it often caused the keyboard to freeze. This should no longer happen, but if it does, removing the patch should suffice.

Some useful commands for developing keyboard patches:

- remove the patch: /usr/sbin/patchmanager -u sfos-patch-keyboard-toggle-prediction

- restart the keyboard: systemctl --user restart maliit-server

- reset settings: dconf reset /patch/ichthyosaurus/keyboard-toggle-prediction/enabled

Sources: https://github.com/ichthyosaurus/sailfish-public-patch-sources

Discussion: https://openrepos.net/content/ichthyosaurus/patch-toggle-text-prediction