Fix lifetime issue with EventEngine endpoint wrapper. Before, we woul…

…d delete the wrapper in `grpc_take_wrapped_event_engine_endpoint`, which could destroy the wrapper before the refs became zero and lead to use-after-free / illegal instruction / segfault errors if callbacks return after the wrapper is destroyed. Now, we unref the wrapper instead of explicitly deleting it.

PiperOrigin-RevId: 705673089

src/core/lib/iomgr/event_engine_shims/endpoint.cc

@@ -443,7 +443,7 @@ std::unique_ptr<EventEngine::Endpoint> grpc_take_wrapped_event_engine_endpoint(
       reinterpret_cast<EventEngineEndpointWrapper::grpc_event_engine_endpoint*>(
           ep);
   auto endpoint = eeep->wrapper->ReleaseEndpoint();
-  delete eeep->wrapper;
+  eeep->wrapper->Unref();
   return endpoint;
 }