Fix BodySystem and Gibbing (#20460)

* Fix gibbing & body system

Makes it so that bodies no longer have two sets of torso organs and that gibbed bodies get spread around on the floor again.

* Actually fix the double torso problem

* rootSlot in cameFrom

* Remove SetCoordinates inside GibBody()

* Don't use entity.RandomOffset() in GibBody()

* Gibbing now uses _random.NextVector2()

Content.Shared/Body/Prototypes/BodyPrototype.cs

@@ -1,5 +1,4 @@
-using Robust.Shared.Prototypes;
-using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom.Prototype;
+using Robust.Shared.Prototypes;
 
 namespace Content.Shared.Body.Prototypes;
 

Content.Shared/Body/Systems/SharedBodySystem.Body.cs

@@ -1,4 +1,4 @@
-using System.Linq;
+using System.Linq;
 using System.Numerics;
 using Content.Shared.Body.Components;
 using Content.Shared.Body.Organ;
@@ -156,6 +156,7 @@ public partial class SharedBodySystem
 
         // Child -> Parent connection.
         var cameFrom = new Dictionary<string, string>();
+        cameFrom[rootSlot] = rootSlot;
         // Maps slot to its relevant entity.
         var cameFromEntities = new Dictionary<string, EntityUid>();
         cameFromEntities[rootSlot] = rootPartId;

Content.Shared/Body/Systems/SharedBodySystem.cs

@@ -1,4 +1,4 @@
-using Content.Shared.Damage;
+using Content.Shared.Damage;
 using Content.Shared.Movement.Systems;
 using Content.Shared.Standing;
 using Robust.Shared.Containers;
@@ -50,7 +50,7 @@ public abstract partial class SharedBodySystem : EntitySystem
         // This is blursed
         var slotIndex = containerSlotId.IndexOf(PartSlotContainerIdPrefix, StringComparison.Ordinal);
 
-        if (slotIndex < -1)
+        if (slotIndex < 0)
             return null;
 
         var slotId = containerSlotId.Remove(slotIndex, PartSlotContainerIdPrefix.Length);