text-input: copy over v3 to v4

v4 will be used for iterating over the protocol.
Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Roman Gilg <subdiff@gmail.com>
Reviewed-by: Dorota Czaplejewicz <dorota.czaplejewicz@puri.sm>

Makefile.am

@@ -6,6 +6,7 @@ unstable_protocols =								\
 	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/text-input/text-input-unstable-v4.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				\