Summary:
depends from D9521

listens to switch events and updates the tablet mode status
which is exposed to dbus in the org.kde.KWin.TabletModeManager
interface

Test Plan:
as hardware support is limited, testing of clients
so far is done by the setter in the dbus property,
which should be removed from the final version.
It has been tested to successfully work on a Thinkpad.

Reviewers: #plasma, #kwin, graesslin

Reviewed By: #plasma, #kwin, graesslin

Subscribers: graesslin, davidedmundson, plasma-devel, kwin, #kwin

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D9764