Move StackLayout tests from qtquickcontrols.git (5.15)

In 5.15 branch, there were still some autotests for StackLayout lurking
around in the qtquickcontrols repo that wasn't moved to declarative for
some reason. Move them to qtdeclarative repo. One of these tests also
demonstrated a genuine failure, so we want to keep these tests.
(It is currently skip()ped)

(Moved from tests/auto/controls/data/tst_stacklayout.qml)

Pick-to: 6.4 6.2 5.15
Change-Id: I826228625c9f15b6028ad881adfc5370bdd17ca1
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>