win: use modern API

Zhao Yuhang

2023-12-22 adb46e1e151b73e56a7e0066a896b48b92a7230e

 src/widgets/widgetwindowagent.cpp

@@ -36,9 +36,7 @@
        w->setAttribute(Qt::WA_DontCreateNativeAncestors);
        w->setAttribute(Qt::WA_NativeWindow);

        if (!d->setup(w, new WidgetItemDelegate())) {
            return false;
        }
        d->setup(w, new WidgetItemDelegate());
        d->hostWidget = w;

#ifdef Q_OS_WINDOWS