Implement Every & Some aggregate types using attached properties

Could be useful with for a group of delegates which are all instantiated at once without having to modify the model or to implement a proxy model on top. Not quite suitable for item views where delegates are only partially instantiated though.

Sample usage: aggregate-hovered.qml

pragma ComponentBehavior: Bound

import QtQuick
import org.kde.kitemmodels as KItemModels

Rectangle {
    id: root

    width: 550
    height: 500
    color: "#000"  // elevation 0

    palette.highlight: "#1570A7"

    KItemModels.KAggregateSome {
        id: aggregate
    }

    Rectangle {
        anchors.fill: parent
        anchors.margins: 20
        color: "#212121"  // elevation 1
        border.color: palette.highlight
        border.width: hoverHandler.hovered && !aggregate.value ? 3 : 0
        radius: 5

        HoverHandler {
            id: hoverHandler
        }

        Flow {
            anchors.fill: parent
            anchors.margins: 10

            Repeater {
                model: 10

                Item {
                    implicitWidth: 150
                    implicitHeight: 100

                    Rectangle {
                        anchors.fill: parent
                        anchors.margins: 10
                        color: "#303030"  // elevation 3
                        border.color: palette.highlight
                        border.width: hoverHandler.hovered ? 3 : 0
                        radius: 5

                        NumberAnimation on radius {}
                    }

                    HoverHandler {
                        id: hoverHandler

                        KItemModels.KAggregateSome.group: aggregate
                        KItemModels.KAggregateSome.value: hovered
                    }
                }
            }
        }
    }
}