Clutter assumed seat0 which is most usually, but not always correct.
Add an evdev-backend specific function to allow passing the seat
that will be used for ClutterDeviceManager construction, which we
already obtain in MetaLauncher.
https://bugzilla.gnome.org/show_bug.cgi?id=778092
Stylus configuration (stylus buttons, pressure) was handled
at the very high level, doing the button and pressure translations
right before sending these to wayland clients.
However, it makes more sense to store these settings into the
ClutterInputDeviceTool itself, and have clutter apply the config
at the lower level so 1) the settings actually apply desktop-wide,
not just in clients and 2) X11 and wayland may share similar
configuration paths. The settings are now just applied whenever
the tool enters proximity, in reaction to
ClutterDeviceManager::tool-changed.
This commit moves all handling of these two settings to
the clutter level, and removes the wayland-specific paths
https://bugzilla.gnome.org/show_bug.cgi?id=773779
