QQuickWindow should have C++ equivalents for all properties that are exposed in QML Window

Examples:

• z-value was introduced in Window (https://doc-snapshots.qt.io/qt6-6.7/qml-qtquick-window.html#z-prop ) but not in QQuickWindow (which does inherit x and y properties from QWindow).
• The new Window.parent property be either a Window or an Item, but QQuickWindow::setParent() can only accept QWindow and not QQuickItem.