Work on backporting new d-bus functionality from Orca.

src/cthulhu/dbus_service.py

@@ -488,6 +488,23 @@ if _dasbus_available:
             debug.printMessage(debug.LEVEL_INFO, msg, True)
             return result
 
+        def Quit(self) -> bool: # pylint: disable=invalid-name
+            """Quits Cthulhu. Returns True if the quit request was accepted."""
+
+            msg = "DBUS SERVICE: Quit called."
+            debug.printMessage(debug.LEVEL_INFO, msg, True)
+
+            from . import cthulhu  # pylint: disable=import-outside-toplevel
+
+            # cthulhu.shutdown() shuts down the dbus service, so send the response immediately and then
+            # do the actual shutdown after a brief delay.
+            def _delayed_shutdown():
+                cthulhu.shutdown()
+                return False
+
+            GLib.timeout_add(100, _delayed_shutdown)
+            return True
+
         def shutdown_service(self, bus: SessionMessageBus, object_path_base: str) -> None:
             """Releases D-Bus resources held by this service and its modules."""