Set mode in AbstractOutput
Summary:
Set the mode in AbstractOutput and call into the plugin
for final change on hardware.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: davidedmundson, kwin
Tags: KWin
Maniphest Tasks: T10016
Differential Revision: https://phabricator.kde.org/D16786