Shared Containers (#3331)

* Namespace changes for containers.
Moved ContainerSlot from content to engine.

* Merged client/server ContainerManagerComponents into a single shared version.

* Mapfile and nullability fixes.

* Upgrades map.

* Update engine.

Content.Server/GameObjects/Components/Body/BodyComponent.cs

@@ -11,6 +11,7 @@ using Content.Shared.Utility;
 using Robust.Server.Console;
 using Robust.Server.GameObjects;
 using Robust.Shared.Console;
+using Robust.Shared.Containers;
 using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
 using Robust.Shared.Log;
@@ -51,7 +52,7 @@ namespace Content.Server.GameObjects.Components.Body
         {
             base.Initialize();
 
-            _partContainer = ContainerManagerComponent.Ensure<Container>($"{Name}-{nameof(BodyComponent)}", Owner);
+            _partContainer = ContainerHelpers.EnsureContainer<Container>(Owner, $"{Name}-{nameof(BodyComponent)}");
 
             foreach (var (slot, partId) in PartIds)
             {