Draft: Layershell: Panels don't get moved by other panels

Use the new accomodate_exclusive_zones call of LayerShell to stop panels from being automatically moved in order to accomodate other panels: right now the first panel it appears, it "wins" not the most intuitive or reproduceble behavior.

Change it to accomodate the panels client side with the new policy that horizontal panels win against vertical panels, which is more predictable as the same thing will always happen.

Also, is now possible again to have 2 panels on the same line: as before is responsibility of the user to not make them overlap

Depends on kwin!5704 and layer-shell-qt!70

BUG: 489703 FIXED-IN: 6.3.0