Calls lua handlers, then passes the event to the appropriate client
Doesn't do pointer emulation (unlike sway) because in the
GNOME/Gtk worldview that's done client-side, so my assumption is
anything else that wants to co-exist with GNOME also has to
do it client-side
Still to do:
- verify whether return value of the lua handler will affect whether
event passed to child
- clean up the hacky int we use to track whether to set touch
seat capability
Daniel Barlow