KWinRules KCM Redesign

Summary:
Replacement KCM to configure kwin rules, using a QML-based UI.

After some work on the task T12729, it is almost feature-par with the previous module, and adapted to the recent move to KConfigXT.

Test Plan:
{F8208046}
{F8208047}

Reviewers: #plasma, #kwin, #vdg, ngraham, davidedmundson, zzag

Reviewed By: #plasma, #kwin, #vdg, ngraham, davidedmundson, zzag

Subscribers: ngraham, davidedmundson, hchain, broulik, zzag, kwin

Tags: #kwin, #vdg

Differential Revision: https://phabricator.kde.org/D28152