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