[applets/kicker] Fix missing highlight on Dashboard grids & list

Part of the reason was incomplete PlasmaExtras.Highlight refactoring,
other part is anchors not working for highlight instance:

    /usr/share/plasma/plasmoids/org.kde.plasma.kicker/contents/ui/DashboardRepresentation.qml:970:36:
    QML Highlight: Cannot anchor to an item that isn't a parent or sibling.

BUG: 453980


(cherry picked from commit 5638ab14)