use different constructor to more reliably set the parent for menus and actions

This may make rendering menus more stable on hi-dpi monitors.
It worked before, but sometimes it had some weird glitches.

src/mainwindow.py

@@ -67,7 +67,8 @@ class MainWindow(QMainWindow):
         ]
 
         for (menu_id, menu_label) in known_menus:
-            menu = QMenu(menu_label, self)
+            menu = QMenu(self)
+            menu.setTitle(menu_label)
             mcs: [MenuContribution] = [mc for mc in menu_contributions if mc.menu_id == menu_id]
             if len(mcs) == 0:
                 continue