AdwTabView and AdwViewStack have inconsistent accessibility trees
In both AdwTabView and AdwViewStack, the intermediate objects, AdwTabPage and AdwViewStackPage respectively, override get_first_accessible_child to return that object's associated bin or widget. But they don't call get_accessible_parent on the bin/widget. So, for example, if an AdwTabView has two tab pages, then the first child of the first tab page will be the first bin, as it should be, but then that first bin's next sibling will be the second bin, which belongs to the second tab page. So the second bin will be a child of both tab pages, and neither bin will correctly report the intermediate tab page object as its parent.