[A11y] ScreenReader reads QML StackView as "unknown" on windows

Using a QML StackView on Windows leads to a UIA_CustomControlType in the a11y hierarchy.

Every time a new page is pushed onto the stack this element gets focused. Per default NVDA reads the element as "Unknown", which can confuse the user. But even a proper name given by Accessible.name is confusing as it is always read when the current view on the stack changes.

A workaround is setting Accessible.ignored: true on the StackView and forcing the focus on a chosen element or setting Accessible.role: Accessible.Grouping as a more appropriate role.

We propose the default behavior for StackView to be changed to add a UIA_GroupControl element instead of UIA_CustomElement.