Make ghost component ECS (#4159)

* Make ghost component ECS

* Remove players and locations properties from ghost component

* Address reviews

* One more doc

* Fix client ghost component state method error

Content.Shared/Ghost/SharedGhostSystem.cs

@@ -0,0 +1,88 @@
+using System;
+using System.Collections.Generic;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Ghost
+{
+    public abstract class SharedGhostSystem : EntitySystem
+    {
+        public override void Initialize()
+        {
+            base.Initialize();
+
+            SubscribeLocalEvent<SharedGhostComponent, GhostChangeCanReturnToBodyEvent>(OnGhostChangeCanReturnToBody);
+        }
+
+        private void OnGhostChangeCanReturnToBody(EntityUid uid, SharedGhostComponent component, GhostChangeCanReturnToBodyEvent args)
+        {
+            if (component.CanReturnToBody == args.CanReturnToBody)
+            {
+                return;
+            }
+
+            component.CanReturnToBody = args.CanReturnToBody;
+            component.Dirty();
+        }
+    }
+
+    /// <summary>
+    ///     Raised to change the value of <see cref="SharedGhostComponent.CanReturnToBody"/>
+    /// </summary>
+    [Serializable, NetSerializable]
+    public class GhostChangeCanReturnToBodyEvent : EntityEventArgs
+    {
+        public GhostChangeCanReturnToBodyEvent(bool canReturnToBody)
+        {
+            CanReturnToBody = canReturnToBody;
+        }
+
+        public bool CanReturnToBody { get; }
+    }
+
+    [Serializable, NetSerializable]
+    public class GhostWarpsRequestEvent : EntityEventArgs
+    {
+    }
+
+    [Serializable, NetSerializable]
+    public class GhostWarpsResponseEvent : EntityEventArgs
+    {
+        public GhostWarpsResponseEvent(List<string> locations, Dictionary<EntityUid, string> players)
+        {
+            Locations = locations;
+            Players = players;
+        }
+
+        public List<string> Locations { get; }
+
+        public Dictionary<EntityUid, string> Players { get; }
+    }
+
+    [Serializable, NetSerializable]
+    public class GhostWarpToLocationRequestEvent : EntityEventArgs
+    {
+        public string Name { get; }
+
+        public GhostWarpToLocationRequestEvent(string name)
+        {
+            Name = name;
+        }
+    }
+
+    [Serializable, NetSerializable]
+    public class GhostWarpToTargetRequestEvent : EntityEventArgs
+    {
+        public EntityUid Target { get; }
+
+        public GhostWarpToTargetRequestEvent(EntityUid target)
+        {
+            Target = target;
+        }
+    }
+
+    [Serializable, NetSerializable]
+    public class GhostReturnToBodyRequest : EntityEventArgs
+    {
+    }
+}