Por all usages of QWindop/windowHandle to KDDockWidgets::Window

Removes a lot of asQWidget() code and is also prepared for non-Qt
views.

src/qtquick/Window_qtquick.h

@@ -0,0 +1,25 @@
+/*
+  This file is part of KDDockWidgets.
+
+  SPDX-FileCopyrightText: 2020-2022 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
+  Author: Sérgio Martins <sergio.martins@kdab.com>
+
+  SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
+
+  Contact KDAB at <info@kdab.com> for commercial licensing options.
+*/
+
+#pragma once
+
+#include "qtcommon/Window_qt.h"
+
+namespace KDDockWidgets {
+class DOCKS_EXPORT Window_qtquick : public Window_qt
+{
+public:
+    using Window_qt::Window_qt;
+    ~Window_qtquick();
+    std::shared_ptr<ViewWrapper> rootView() const override;
+    Window::Ptr transientParent() const override;
+};
+}