[HLE] Renamed INotificationServicesForSystem and implemented a commands (and stubs)

Should allow Ring Fit to get in-game, needs testing.

src/Ryujinx.HLE/HOS/Services/Notification/INotificationSystemEventAccessor.cs

@@ -0,0 +1,17 @@
+using Ryujinx.Common.Logging;
+
+namespace Ryujinx.HLE.HOS.Services.Notification
+{
+    class INotificationSystemEventAccessor : IpcService
+    {
+        public INotificationSystemEventAccessor(ServiceCtx context) { }
+        
+        [CommandCmif(0)] // 9.0.0+
+        // GetNotificationSendingNotifier() -> nn::notification::server::INotificationSystemEventAccessor
+        public ResultCode GetSystemEvent(ServiceCtx context)
+        {
+            Logger.Stub?.PrintStub(LogClass.Service);
+            return ResultCode.Success;
+        }
+    }
+}