Port KWin to KWaylandServer
Summary: Away from KWayland::Server and KF5WaylandServer.
Test Plan: Builds, ran nested session
Reviewers: KWin, Plasma, Frameworks, davidedmundson, zzag
Reviewed By: KWin, Plasma, davidedmundson, zzag
Subscribers: zzag, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D29278