backend/libinput: use wl_array for wlr_libinput_tablet.tools
backend/libinput: use wl_array for wlr_libinput_tablet.tools

Instead of using a single-field wl_list, let's just use a wl_array.

swaywm/wlroots,SirCmpwn/wlroots,swaywm/wlroots