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

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

src/qtcommon/Platform_qt.cpp

@@ -10,7 +10,9 @@
 */
 
 #include "Platform_qt.h"
+#include "Window_qt.h"
 
+#include <QWindow>
 #include <QGuiApplication>
 
 using namespace KDDockWidgets;
@@ -28,3 +30,22 @@ std::shared_ptr<ViewWrapper> Platform_qt::focusedView() const
 {
     return qobjectAsView(qApp->focusObject());
 }
+
+Window::List Platform_qt::windows() const
+{
+    Window::List windows;
+    const auto qtwindows = qApp->topLevelWindows();
+    windows.reserve(qtwindows.size());
+    for (QWindow *qtwindow : qtwindows) {
+        windows << windowFromQWindow(qtwindow);
+    }
+
+    return windows;
+}
+
+std::shared_ptr<Window> Platform_qt::qobjectAsWindow(QObject *obj) const
+{
+    if (auto window = qobject_cast<QWindow *>(obj))
+        return windowFromQWindow(window);
+    return nullptr;
+}