When running as a native compositor, we can just do that. However, the
previous code must stay for whenever it's run as a X11 client.
Additionally, the fallback switch{} that transforms clutter 1-indexed
buttons into input.h event codes had to be adapted to the change introduced
in clutter commit 83b738c0e, where the 4-7 button range is kept clear for
compatibility with the X11 backend.
https://bugzilla.gnome.org/show_bug.cgi?id=758239
7309b20c25