FakeInput: add support for keyboard key press and release

Summary: Adds support for keyboard button press and release as defined in linux/input-event-codes.h

Reviewers: davidedmundson, apol, #plasma, romangg

Reviewed By: davidedmundson, #plasma

Subscribers: kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D23766