test: rework lib stuff to share common files

test/lib/dispatcher/shared/lib.cpp

@@ -0,0 +1,8 @@
+#include <entt/core/attribute.h>
+#include <entt/signal/dispatcher.hpp>
+#include "types.h"
+
+ENTT_API void trigger(entt::dispatcher &dispatcher) {
+    dispatcher.trigger<event>();
+    dispatcher.trigger(message{42});
+}