wayland: add wayland-extensions functions

add utilities to lock the pointer to a window and to get relative mouse
movement in Wayland. This is made possible thanks to the wayland
protocols introduced in the previous commit.

Code freely taken and adapted from Christophe Fergeau branch:
https://gitlab.freedesktop.org/teuf/spice-gtk/-/tree/wayland



Signed-off-by: Francesco Giudici <fgiudici@redhat.com>
Acked-by: Frediano Ziglio <fziglio@redhat.com>