Add Platform_qt, a baseclass for both Qt frontends

So we can share some code between QtQuick and QtWidgets

src/qtcommon/Platform_qt.h

@@ -0,0 +1,30 @@
+/*
+  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 "docks_export.h"
+#include "Platform.h"
+
+namespace KDDockWidgets {
+
+/// @brief Baseclass platform for Qt based platform
+/// Useful since QtWidgets and QtQuick share some similarities
+class DOCKS_EXPORT Platform_qt : public Platform
+{
+public:
+    Platform_qt();
+    ~Platform_qt() override;
+
+    std::shared_ptr<ViewWrapper> focusedView() const override;
+};
+
+}