StackView a11y double replace crash

With active a11y screenreader on different plattforms the StackView can crash the application. This can occur when replace is called two times in a row from the same object.

This can be demonstrated by having a button call replace in its onClicked method. During the transition to the new page the a11y focus remains on the button on the old page. If the button is then activated again the app crashes, as the old page gets destroyed at the end of the transition. See the attached example.

This problem can be mitigated by checking the StackView.status and only calling replace when the status of the current page is StackView.Active. But there should be either an internal Qt check here or the a11y focus has to be moved to the new page as soon as it is created.