LSP: forcefully close language server after 3 seconds on shutdown

When closing Qt Creator a message is send to the server requesting to
shutdown. Waiting an undefined amount of time for the response could
result in a never closing Qt Creator.

Change-Id: If09a32d34c546ae4702669d65e4921873e5658ea
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/languageclient/languageclientmanager.cpp

@@ -221,6 +221,11 @@ void LanguageClientManager::shutdown()
         else
             deleteClient(interface);
     }
+    QTimer::singleShot(3000, managerInstance, [](){
+        for (auto interface : managerInstance->m_clients)
+            deleteClient(interface);
+        emit managerInstance->shutdownFinished();
+    });
 }
 
 LanguageClientManager *LanguageClientManager::instance()