Abstract OutputDevice initialization
Summary:
Move generic Wayland parts of OutputDevice initialization into
AbstractOutput class.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: davidedmundson, kwin
Tags: KWin
Maniphest Tasks: T10016
Differential Revision: https://phabricator.kde.org/D16789