text-input: Add v3 of the text-input protocol

This new protocol description is an evolution of v2.

- All pre-edit text styling is gone.
- Pre-edit cursor can span characters.
- No events regarding input panel (OSK) state nor covered rectangle.
  Compositors are still free to handle situations where the keyboard
  focus rectangle is covered by the input panel.
- No set_preferred_language request for clients.
- There is no event to send keysyms. Compositors can use wl_keyboard
  interface instead.
- All state is double-buffered, with specified defaults.
- The compositor can be notified about external changes to the state.
- The client can detect outdated requests.

Signed-off-by: Dorota Czaplejewicz <dorota.czaplejewicz@puri.sm>
Signed-off-by: Carlos Garnacho <carlosg@gnome.org>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Simon Ser <contact@emersion.fr>

Makefile.am

@@ -5,6 +5,7 @@ unstable_protocols =								\
 	unstable/fullscreen-shell/fullscreen-shell-unstable-v1.xml		\
 	unstable/linux-dmabuf/linux-dmabuf-unstable-v1.xml			\
 	unstable/text-input/text-input-unstable-v1.xml				\
+	unstable/text-input/text-input-unstable-v3.xml				\
 	unstable/input-method/input-method-unstable-v1.xml			\
 	unstable/xdg-shell/xdg-shell-unstable-v5.xml				\
 	unstable/xdg-shell/xdg-shell-unstable-v6.xml				\