Add system to CompNetworkGenerator (#4310)

Robust doesn't global using this but content does so any automatic comp states on engine don't work.

Robust.Shared.CompNetworkGenerator/ComponentNetworkGenerator.cs

@@ -148,6 +148,7 @@ namespace Robust.Shared.CompNetworkGenerator
             }
 
             return $@"// <auto-generated />
+using System;
 using Robust.Shared.GameStates;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Analyzers;