Turns GameTicker into an EntitySystem. (#4197)

* GameTicker turned into an EntitySystem

* Turns ClientGameTicker into an EntitySystem, turn NetMessages into events

* Change event names to be more consistent with the rest.

* YAML linter uses the dummy gameticker CVar override.

* Fix game ticker initialization order

* Dummy ticker won't spawn players.

* Fix character creation test

Content.Server/Chat/Commands/SuicideCommand.cs

@@ -125,7 +125,7 @@ namespace Content.Server.Chat.Commands
 
             // Prevent the player from returning to the body.
             // Note that mind cannot be null because otherwise owner would be null.
-            IoCManager.Resolve<IGameTicker>().OnGhostAttempt(mind!, false);
+            EntitySystem.Get<GameTicker>().OnGhostAttempt(mind!, false);
         }
     }
 }