[Reg 5.15 -> 6.2] Item ignores the initial size from a binding when implicit size is used with Behavior

The issue title may be a bit confusing. It's simpler to show on a minimal example.

import QtQuick 2.0

Item
{
    width: 400
    height: 400

    Rectangle
    {
        color: "yellow"
        implicitWidth: 50
        implicitHeight: 50
        height: { return 0 }
        Behavior on height { NumberAnimation { duration: 300 } }
    }
}

There's implicitHeight set for the Rectangle. Also height is set to be zero via a binding. The expected height of the item in this case is 0. But if there's  a Behavior on height, the initial value from the binding is not applied and the resulting height is 50.

In Qt 5 the issue does not exist, and the resulting item height is 0.

Some details:

• It does not matter what the binding returns. It may be 0, it may be 12345. Any value is ignored.
• The binding is not killed by something. If its value could be changed, the Behavior will animate the height. For example I can declare a property, bind height to its value, and later change the property. The Behavior will play the animation.