Make sure that QCocoaWindowManager is initialized in static builds

If code has no external references, then with a static build of Qt the
linker is free to strip those object files from the final executable.
This is what happened with QCocoaWindowManager, which had no exported
symbols, and no callers from other files.

To prevent the linker from stripping the object file and to ensure that
the constructor function gets called during startup, move that
function declaration to the QCocoaIntegration code, which is always
loaded.

Fixes: QTBUG-99280
Pick-to: 6.2 6.3
Change-Id: Icdafea372a1b42c6ecdb43e36aeb0a04a70e3d4e
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/plugins/platforms/cocoa/qcocoaintegration.mm

@@ -57,6 +57,7 @@
 #if QT_CONFIG(sessionmanager)
 #  include "qcocoasessionmanager.h"
 #endif
+#include "qcocoawindowmanager.h"
 
 #include <qpa/qplatforminputcontextfactory_p.h>
 #include <qpa/qplatformaccessibility.h>
@@ -81,6 +82,11 @@ QT_BEGIN_NAMESPACE
 
 Q_LOGGING_CATEGORY(lcQpa, "qt.qpa", QtWarningMsg);
 
+// Lives here so that the linker is forced to include the QCocoaWindowManager
+// object file also in static builds.
+static void initializeWindowManager() { Q_UNUSED(QCocoaWindowManager::instance()); }
+Q_CONSTRUCTOR_FUNCTION(initializeWindowManager)
+
 static void logVersionInformation()
 {
     if (!lcQpa().isInfoEnabled())

src/plugins/platforms/cocoa/qcocoawindowmanager.mm

@@ -116,8 +116,5 @@ void QCocoaWindowManager::modalSessionChanged()
     }
 }
 
-static void initializeWindowManager() { Q_UNUSED(QCocoaWindowManager::instance()); }
-Q_CONSTRUCTOR_FUNCTION(initializeWindowManager)
-
 QT_END_NAMESPACE