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/GameTicking/GameTicker.StatusShell.cs

@@ -0,0 +1,34 @@
+using Newtonsoft.Json.Linq;
+using Robust.Server.ServerStatus;
+using Robust.Shared.IoC;
+
+namespace Content.Server.GameTicking
+{
+    public partial class GameTicker
+    {
+        /// <summary>
+        ///     Used for thread safety, given <see cref="IStatusHost.OnStatusRequest"/> is called from another thread.
+        /// </summary>
+        private readonly object _statusShellLock = new();
+
+        private void InitializeStatusShell()
+        {
+            IoCManager.Resolve<IStatusHost>().OnStatusRequest += GetStatusResponse;
+        }
+
+        private void GetStatusResponse(JObject jObject)
+        {
+            // This method is raised from another thread, so this better be thread safe!
+            lock (_statusShellLock)
+            {
+                jObject["name"] = _baseServer.ServerName;
+                jObject["players"] = _playerManager.PlayerCount;
+                jObject["run_level"] = (int) _runLevel;
+                if (_runLevel >= GameRunLevel.InRound)
+                {
+                    jObject["round_start_time"] = _roundStartTime.ToString("o");
+                }
+            }
+        }
+    }
+}