qtquick: Make Window_qtquick::rootView() behave like in v 1.x

The MainWindow might not be the QQuickView's root item, but
version 1.x would still return that. So preserve that, since it's
what tests expect.

We can improve after having tests passing.

src/qtquick/Window_qtquick.cpp

@@ -22,14 +22,38 @@ Window_qtquick::~Window_qtquick()
 {
 }
 
+inline View *topMostKDDWView(QQuickItem *parent)
+{
+    if (!parent)
+        return {};
+
+    if (auto v = qobject_cast<Views::View_qtquick *>(parent))
+        return v;
+
+    const auto children = parent->childItems();
+    for (QQuickItem *item : children) {
+        if (auto v = topMostKDDWView(item))
+            return v;
+    }
+
+    return nullptr;
+}
+
 std::shared_ptr<ViewWrapper> Window_qtquick::rootView() const
 {
     if (auto quickwindow = qobject_cast<QQuickWindow *>(m_window)) {
         auto contentItem = quickwindow->contentItem();
-        const auto children = contentItem->childItems();
-        Q_ASSERT(!children.isEmpty());
+        if (View *view = topMostKDDWView(contentItem)) {
+            // This block is for retrocompatibility with 1.x. For QtQuick the topmost "widget" is a KDDW known widget
+            // and not any arbitrary user QtQuickItem.
+            // TODOm3: I'd like to change it so it's normalized.
+            return view->asWrapper();
+        } else {
+            const auto children = contentItem->childItems();
+            Q_ASSERT(!children.isEmpty());
 
-        return Views::asQQuickWrapper(contentItem->childItems().first());
+            return Views::asQQuickWrapper(contentItem->childItems().first());
+        }
     } else {
         qWarning() << Q_FUNC_INFO << "Expected QQuickView";
     }