Provide a fake approach to tablet event propagation

Summary:
At the moment, the state of wayland of getting such events isn't all
that clear. There's a zwp_tablet protocol that isn't stable yet and more
importantly isn't supported by Qt just yet.
Have it move and click the mouse about for now.

Depends on D25663 and D25763

Reviewers: #kwin, romangg

Reviewed By: #kwin, romangg

Subscribers: romangg, zzag, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D25764