gpu: Use std::jthread for async gpu thread

src/core/core.cpp

@@ -305,10 +305,7 @@ struct System::Impl {
         is_powered_on = false;
         exit_lock = false;
 
-        if (gpu_core) {
-            gpu_core->ShutDown();
-        }
-
+        gpu_core.reset();
         services.reset();
         service_manager.reset();
         cheat_engine.reset();
@@ -317,7 +314,6 @@ struct System::Impl {
         time_manager.Shutdown();
         core_timing.Shutdown();
         app_loader.reset();
-        gpu_core.reset();
         perf_stats.reset();
         kernel.Shutdown();
         memory.Reset();