Remove uses of TransformComponent.ChildEntities (#22442)

* Make output of ChildEnumerator non-nullable

* Remove uses of ChildEntities

* poke tests

---------

Co-authored-by: metalgearsloth <comedian_vs_clown@hotmail.com>

Content.Server/Cargo/Systems/CargoSystem.Shuttle.cs

@@ -292,7 +292,7 @@ public sealed partial class CargoSystem
         var children = xform.ChildEnumerator;
         while (children.MoveNext(out var child))
         {
-            if (!CanSell(child.Value, _xformQuery.GetComponent(child.Value)))
+            if (!CanSell(child, _xformQuery.GetComponent(child)))
                 return false;
         }