Summary:
Workspace monitors the X11 events to detect when the user first
interacts with the system. This is only required on X11 for activating
the same client from previous session. So far this was spread over many
parts in the long event switch statement. To make this more contained a
dedicated event filter is introduced which also gets deleted again once
the first user interaction got recognized.

Test Plan: Compiles

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D7371