Require a message on "Application::signalStop" (#5255)

This change adds a message parameter to Application::signalStop for extra context.

src/test/jtx/impl/Env.cpp

@@ -96,7 +96,7 @@ Env::AppBundle::~AppBundle()
     if (app)
     {
         app->getJobQueue().rendezvous();
-        app->signalStop();
+        app->signalStop("~AppBundle");
     }
     if (thread.joinable())
         thread.join();