Replaced InputEventFilter by InputEventSpy in DebugConsole

Summary:
As explained in 84e33081
the DebugConsole should use an InputEventSpy instead of an InputEventFilter.

Reviewers: kwin, graesslin

Reviewed By: graesslin

Subscribers: graesslin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D3879