QQuickTextNode carries high fixed memory cost

m_currentLineTree in QQuickTextNodeEngine is close to 32K in size. This adds significant fixed overhead when there are a large number of Text elements.

For example, massif reports 50MB of heap usage for the following example:

import QtQuick 2.0

Grid {
    width: 400; height: 400
    rows: 40; columns: 40
    Repeater {
        model: rows*columns
        delegate: Text { width: 10; height: 10; text: "a" }
    }
}