Introduce the concept of an internal window system independent id

Summary:
For supporting Wayland windows in the kwin_rules_dialog we need a way to
pass a window id for Wayland windows to the dialog. This id needs to be
sent to the dbus interface to query window information just like the
interactive query. For Wayland windows we don't really have a window id
and it would require to also pass the windowing system to
kwin_rules_dialog and back through the dbus interface.

To not complicate things this change introduces a windowing system
independent id based on UUID. This could in future also be used
internally for areas where it's window id based and used in both
windowing systems.

Test Plan: Adjusted test cases to verify the uuid is generated and passed to Deleted

Reviewers: #kwin

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16986