Summary:
Windows no longer needs a separate plugin, and X11 and Wayland are now in
separate files instead of having lots of ifdefs.
Test Plan: Tested on X11, Wayland and Windows.
Reviewers: #kde_connect, apol, nicolasfella
Reviewed By: #kde_connect, apol, nicolasfella
Subscribers: apol, nicolasfella
Tags: #kde_connect
Differential Revision: https://phabricator.kde.org/D11692
