test: rework lib stuff to share common files

test/lib/locator/shared/lib.cpp

@@ -0,0 +1,11 @@
+#include <entt/core/attribute.h>
+#include <entt/locator/locator.hpp>
+#include "types.h"
+
+ENTT_API void set_up(const entt::locator<service>::node_type &handle) {
+    entt::locator<service>::reset(handle);
+}
+
+ENTT_API void use_service(int value) {
+    entt::locator<service>::value().value = value;
+}