Tablet tool settings are not instant apply
Currently MetaInputSettings only applies stylus settings when
ClutterDeviceManager::tool-changed is emitted (that is, when a stylus begins/stops driving a device). This is generally sufficient, but gives a bad look&feel while modifying stylus settings on g-c-c.
It seems feasible to keep track of the currently active tool(s), so we can apply configuration changes in those instantly.