logind: Add a function that detects the logind seat.
Summary:
This will allow other parts of kwin to get the current logind seat that this instance is running under
Reviewers: KWin, graesslin
Reviewed By: KWin, graesslin
Subscribers: graesslin, anthonyfieroni, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D9551