Summary:
This dbus method is intended to be used by the kwin rules dialog. KWin
can pass the internal id to the rules dialog through a command line
argument (or similar way) and the dialog can query the information
through the dbus call for the provided id. Thus it's possible to
implement one way to query the information which works on both X11 and
Wayland without any windowing system specific functionality.

Test Plan: See new added integration test

Reviewers: #kwin

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D17433