Summary:
A protocol that attaches to a surface and contains two strings which can
change.
The intended use is for clients to link a DBus Appmenu object with a
surface.
This is in preparation for the Qt Extended Surface deprecation which
currently handles this in Kwin.
Test Plan: Attached unit test
Reviewers: #plasma, graesslin
Reviewed By: #plasma, graesslin
Subscribers: broulik, graesslin, plasma-devel, #frameworks
Tags: #frameworks, #plasma_on_wayland
Differential Revision: https://phabricator.kde.org/D8919
