This moves the unicode input start / end sequences into their own
functions, so keymaps and other functionality can build on it too.
At the same time, it changes how the Linux variant works, to match
reality: CTRL+SHIFT must be unregistered too, and we close the thing
with a Space instead.
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
63e5782d2c