Add a suffix to the window title when running from a debug build

Since projects started from the editor or exported in debug mode
run slower than those exported in release mode, this should be
clearly presented to the user.

This partially addresses #20219.

(cherry picked from commit a9c60007a9f7cacd690c09b7f74a5e6f190c5cfb)

main/main.cpp

@@ -1825,7 +1825,14 @@ bool Main::start() {
 			sml->set_quit_on_go_back(GLOBAL_DEF("application/config/quit_on_go_back", true));
 			String appname = ProjectSettings::get_singleton()->get("application/config/name");
 			appname = TranslationServer::get_singleton()->translate(appname);
+#ifdef DEBUG_ENABLED
+			// Append a suffix to the window title to denote that the project is running
+			// from a debug build (including the editor). Since this results in lower performance,
+			// this should be clearly presented to the user.
+			OS::get_singleton()->set_window_title(vformat("%s (DEBUG)", appname));
+#else
 			OS::get_singleton()->set_window_title(appname);
+#endif
 
 			int shadow_atlas_size = GLOBAL_GET("rendering/quality/shadow_atlas/size");
 			int shadow_atlas_q0_subdiv = GLOBAL_GET("rendering/quality/shadow_atlas/quadrant_0_subdiv");