client: implement QWaylandScreen::topLevelAt()

For security reason, Wayland doesn't provide global position for
top level windows in most cases.

Task-number: QTBUG-113404
Pick-to: 6.7 6.5 6.2 5.15
Change-Id: I2cd11b641fba6582cf96cfbea16f5e598a473db5
Reviewed-by: David Edmundson <davidedmundson@kde.org>

src/plugins/platforms/wayland/qwaylandscreen.cpp

@@ -170,6 +170,16 @@ QList<QPlatformScreen *> QWaylandScreen::virtualSiblings() const
     return list;
 }
 
+QWindow *QWaylandScreen::topLevelAt(const QPoint & pos) const
+{
+    if (QWaylandWindow::fixedToplevelPositions) {
+        Q_UNUSED(pos);
+        return nullptr;
+    }
+
+    return QPlatformScreen::topLevelAt(pos);
+}
+
 Qt::ScreenOrientation QWaylandScreen::orientation() const
 {
     return m_orientation;

src/plugins/platforms/wayland/qwaylandscreen_p.h

@@ -63,6 +63,8 @@ public:
     QDpi logicalDpi() const override;
     QList<QPlatformScreen *> virtualSiblings() const override;
 
+    QWindow *topLevelAt(const QPoint &point) const override;
+
     Qt::ScreenOrientation orientation() const override;
     int scale() const;
     qreal devicePixelRatio() const override;