macOS: Track menu bar clicks for popup closing in QCocoaIntegration

A static member in QCocoaMenuBar relies on the app having at least
one QCocoaMenuBar, and also stays around after the qGuiApp has gone
away, potentially leading to a crash.

As a drive-by, clarify the comment and variable name to point out
that we're closing popups on _any_ native menu opening, not just
menus in the main menu bar (NSApp.mainMenu).

Pick-to: 6.7 6.5
Change-Id: Ib14919e317d70e4c76f3d89c78331edb958bf048
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit daad2b28fdb884e6d796ab024bcb962155cf5534)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/plugins/platforms/cocoa/qcocoaintegration.h

@@ -119,6 +119,8 @@ private:
 #endif
 
     QCocoaWindowManager m_windowManager;
+
+    QMacNotificationObserver m_menuTrackingObserver;
 };
 
 Q_DECLARE_OPERATORS_FOR_FLAGS(QCocoaIntegration::Options)

src/plugins/platforms/cocoa/qcocoaintegration.mm

@@ -168,6 +168,12 @@ QCocoaIntegration::QCocoaIntegration(const QStringList &paramList)
 
     connect(qGuiApp, &QGuiApplication::focusWindowChanged,
         this, &QCocoaIntegration::focusWindowChanged);
+
+    // Opening of a native menu should close all popup windows
+    m_menuTrackingObserver = QMacNotificationObserver(nil,
+        NSMenuDidBeginTrackingNotification, ^{
+            QGuiApplicationPrivate::instance()->closeAllPopups();
+        });
 }
 
 QCocoaIntegration::~QCocoaIntegration()

src/plugins/platforms/cocoa/qcocoamenubar.mm

@@ -25,11 +25,6 @@ QCocoaMenuBar::QCocoaMenuBar()
 {
     static_menubars.append(this);
 
-    // clicks into the menu bar should close all popup windows
-    static QMacNotificationObserver menuBarClickObserver(nil, NSMenuDidBeginTrackingNotification, ^{
-        QGuiApplicationPrivate::instance()->closeAllPopups();
-    });
-
     m_nativeMenu = [[NSMenu alloc] init];
     qCDebug(lcQpaMenus) << "Constructed" << this << "with" << m_nativeMenu;
 }