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/Body/BodyComponent.cs

@@ -25,7 +25,6 @@ namespace Content.Server.Body
     public class BodyComponent : SharedBodyComponent, IRelayMoveInput, IGhostOnMove
     {
         private Container _partContainer = default!;
-        [Dependency] private readonly IGameTicker _gameTicker = default!;
 
         protected override bool CanAddPart(string slotId, SharedBodyPartComponent part)
         {
@@ -94,7 +93,7 @@ namespace Content.Server.Body
                 Owner.TryGetComponent(out MindComponent? mind) &&
                 mind.HasMind)
             {
-                 _gameTicker.OnGhostAttempt(mind.Mind!, true);
+                 EntitySystem.Get<GameTicker>().OnGhostAttempt(mind.Mind!, true);
             }
         }