Fix accessibility ancestor tree

Fix accessibility ancestor tree

Before this commit, KItemListViewAccessible would always return
nullptr as its parent. This meant that accessibility software would
have to guess to which window/hierarchy the KItemListView belongs
to. Guessing shouldn't be necessary here.

This commit makes sure that the KItemListView always returns a
sensible parent in the accessible hierarchy. It does so by
explicitly setting the accessible parent for every KItemListView
after construction in the DolphinView contructor. Since
KItemListView now always knows about its accessible parent, the
accessibleInterfaceFactory can always ask the KItemListView for
that information when constructing the QAccessibleInterfaces.

Fixes https://invent.kde.org/system/dolphin/-/issues/47.