Add Platform_qtquick

CMake hacked for now. Not sure if we should allow building
both QtWidgets and QtQuick frontends at the same time

src/qtquick/Platform_qtquick.cpp

@@ -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.
+*/
+
+#include "Platform_qtquick.h"
+#include "KDDockWidgets.h"
+
+static KDDockWidgets::Platform_qtquick s_platformQtQuick;
+
+using namespace KDDockWidgets;
+
+Platform_qtquick::Platform_qtquick()
+{
+}
+
+Platform_qtquick::~Platform_qtquick()
+{
+}
+
+const char *Platform_qtquick::name() const
+{
+    return "qtquick";
+}