Fix high-dpi and QScreen state initialization

Fix bug where QScreen::geometry() returns incorrect
(unscaled) geometry.

We maintain state:

  - QHighDpiScaling::m_active, which is set to true
    if any screen in QGuiApplication::screens() has a
    scale factor > 1, in updateHighDpiScaling()
  - QScreen::m_geometry, which is assigned the scaled
    screen size in QScreenPrivate::updateHighDpi()

Now the problem is that updateHighDpiScaling() requires
an up-to date screens list, and that updateHighDpi()
requires an up-to date m_active, and that currently
updateHighDpi() is called when constructing the QScreen
only.

This is all a bit unsatisfactory, but for now fix this
in the simplest way by adding a second call to
updateHighDpi() in handleScreenAdded(), after the call
to updateHighDpiScaling().

Pick-to: 6.2 6.3
Fixes-number: QTBUG-101601
Change-Id: I5f442ceb966c77d6746ee885203b67da96612587
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/gui/kernel/qwindowsysteminterface.cpp

@@ -43,6 +43,7 @@
 #include "private/qevent_p.h"
 #include "private/qeventpoint_p.h"
 #include "private/qpointingdevice_p.h"
+#include "private/qscreen_p.h"
 #include <QAbstractEventDispatcher>
 #include <qpa/qplatformintegration.h>
 #include <qdebug.h>
@@ -785,6 +786,7 @@ void QWindowSystemInterface::handleScreenAdded(QPlatformScreen *ps, bool isPrima
 
     QGuiApplicationPrivate::resetCachedDevicePixelRatio();
     QHighDpiScaling::updateHighDpiScaling();
+    screen->d_func()->updateHighDpi();
 
     emit qGuiApp->screenAdded(screen);