Do not hard runtime depend on X11 in RuleBook
Summary:
The RuleBook is created during Workspace startup, so it's a required
component for the overall KWin session. It uses a KXMessages object which
means it has a hard X11 runtime dependency.
This change makes the dependency optional and creates the KXMessages once
X11 is available.
Test Plan: Compiles
Subscribers: plasma-devel, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D7653