protocol: add repeat_info event to wl_keyboard

In the process wl_keyboard's version has been incremented. Given
clients get the wl_keyboard from wl_seat without a version, wl_seat's
version has also been incremented (wl_seat version 4 implies
wl_keyboard version 4).

earlier Acked-by: Daniel Stone <daniel@fooishbar.org>
Reviewed-by: Pekka Paalanen <ppaalanen@gmail.com>