Sway has basic support for drawing tablets, but does not expose
properties such as pressure sensitivity. This implements the wlr tablet
v2 protocol, providing tablet events to Wayland clients.
This change mimics the wlroots protocol meson.build. It replaces
meson generators with custom_targets, which will only run wayland-scanner
once per output file.
The idle protocol is not used by any clients, so its client protocol
header is not generated.
The check for the availability of the private-code scanner options has
been removed, since the wlroots dependency requires wayland >= 1.16.
Swayidle handles idle events and allows
for dpms and lockscreen handling. It also
handles systemd sleep events, and can
raise a lockscreen on sleep
Fixes#541
