kwinrules: Limit hightlight scrolling duration

By default, the rules list moves to the hightlighted item
(the one being edited) with a constant velocity. This can
be too slow when the list contains hundreds of items.

By setting `highlightMoveDuration` we set a maximum limit
for this animation.

BUG: 428139

(cherry picked from commit cfeca03e48)

kcmkwin/kwinrules/package/contents/ui/RulesList.qml

@@ -48,6 +48,8 @@ ScrollViewKCM {
             sourceComponent: ruleBookDelegate
         }
 
+        highlightMoveDuration: Kirigami.Units.longDuration
+
         displaced: Transition {
             NumberAnimation { properties: "y"; duration: Kirigami.Units.longDuration }
         }