Material style controls cost excessive memory

As described in mail group (https://lists.qt-project.org/pipermail/interest/2021-May/037055.html), material controls cost excessive memory than normal controls.

When drawing 500 buttons, normal style controls cost 30.9MB memory while material style cost 550MB (on qt 5.12.2, they are 21.6MB and  1GB respectively).

The test code is as:

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.12

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    Repeater {
        model: 500
        Button {
            x: index * 20
            width: 100
            height: 100
        }
    }
}

And style is switched on/off in qtquickcontrols2.conf