Windows QPA: Emulate aboutToHide(), aboutToShow() signals of QPlatformMenu

Wrap the call to TrackPopupMenu accordingly.

Complements 7849aa6e96.

Task-number: QTBUG-64628
Change-Id: Ia370e566266e96ab690ce5ed41d06dea7cafd4e4
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

src/plugins/platforms/windows/qwindowsmenu.cpp

@@ -686,9 +686,16 @@ void QWindowsPopupMenu::showPopup(const QWindow *parentWindow, const QRect &targ
 bool QWindowsPopupMenu::trackPopupMenu(HWND windowHandle, int x, int y)
 {
     lastShownPopupMenu = this;
-    return TrackPopupMenu(menuHandle(),
+    // Emulate Show()/Hide() signals. Could be implemented by catching the
+    // WM_EXITMENULOOP, WM_ENTERMENULOOP messages; but they do not carry
+    // information telling which menu was opened.
+    emit aboutToShow();
+    const bool result =
+        TrackPopupMenu(menuHandle(),
                           QGuiApplication::layoutDirection() == Qt::RightToLeft ? UINT(TPM_RIGHTALIGN) : UINT(0),
                           x, y, 0, windowHandle, nullptr) == TRUE;
+    emit aboutToHide();
+    return result;
 }
 
 bool QWindowsPopupMenu::notifyTriggered(uint id)