Make QCursor::setPos() use the correct screen

setPos() takes a screen argument, however this argument
indicates which cursor should be moved only and is
not usable as an argument to toNativePixels() since
the position may be on a sibling screen.

Add call to QScreen::virtualSiblingAt to get the target
screen.

Task-number: QTBUG-99009
Pick-to: 6.3 6.2 5.15
Change-Id: I8714ebc93a283c58bc67911315f787c484fb0dd8
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/gui/kernel/qcursor.cpp

@@ -251,7 +251,8 @@ void QCursor::setPos(QScreen *screen, int x, int y)
 {
     if (screen) {
         if (QPlatformCursor *cursor = screen->handle()->cursor()) {
-            const QPoint devicePos = QHighDpi::toNativePixels(QPoint(x, y), screen);
+            const QPoint pos(x, y);
+            const QPoint devicePos = QHighDpi::toNativePixels(pos, screen->virtualSiblingAt(pos));
             // Need to check, since some X servers generate null mouse move
             // events, causing looping in applications which call setPos() on
             // every mouse move event.

tests/auto/gui/kernel/qhighdpi/tst_qhighdpi.cpp

@@ -76,6 +76,8 @@ private slots:
     void mouseEvents();
     void mouseVelocity();
     void mouseVelocity_data();
+    void setCursor();
+    void setCursor_data();
 };
 
 /// Offscreen platform plugin test setup
@@ -805,5 +807,22 @@ void tst_QHighDpi::mouseVelocity()
     }
 }
 
+void tst_QHighDpi::setCursor_data()
+{
+    standardScreenDpiTestData();
+}
+
+void tst_QHighDpi::setCursor()
+{
+    QFETCH(QList<qreal>, dpiValues);
+    std::unique_ptr<QGuiApplication> app(createStandardOffscreenApp(dpiValues));
+
+    for (QScreen *screen : app->screens()) {
+        QPoint center = screen->geometry().center();
+        QCursor::setPos(center.x(), center.y());
+        QCOMPARE(QCursor::pos(), center);
+    }
+}
+
 #include "tst_qhighdpi.moc"
 QTEST_APPLESS_MAIN(tst_QHighDpi);