qt: Add ObjectInvoke template function

This is a replacement of the QMetaObject::invokeMethod functor overload
which is available in Qt 5.10+.

Co-authored-by: Russell Yanofsky <russ@yanofsky.org>

src/qt/guiutil.h

@@ -340,6 +340,18 @@ namespace GUIUtil
     #endif
     }
 
+    /**
+     * Queue a function to run in an object's event loop. This can be
+     * replaced by a call to the QMetaObject::invokeMethod functor overload after Qt 5.10, but
+     * for now use a QObject::connect for compatibility with older Qt versions, based on
+     * https://stackoverflow.com/questions/21646467/how-to-execute-a-functor-or-a-lambda-in-a-given-thread-in-qt-gcd-style
+     */
+    template <typename Fn>
+    void ObjectInvoke(QObject* object, Fn&& function, Qt::ConnectionType connection = Qt::QueuedConnection)
+    {
+        QObject source;
+        QObject::connect(&source, &QObject::destroyed, object, std::forward<Fn>(function), connection);
+    }
 
 } // namespace GUIUtil