Make MappingDataNode use string keys (#36111)

* MappingDataNode string keys

* a

* poke

Content.Shared/Containers/ContainerFillComponent.cs

@@ -49,13 +49,11 @@ public sealed class ContainerFillSerializer : ITypeValidator<Dictionary<string,
 
         foreach (var (key, val) in node.Children)
         {
-            var keyVal = serializationManager.ValidateNode<string>(key, context);
-
             var listVal = (val is SequenceDataNode seq)
                 ? ListSerializer.Validate(serializationManager, seq, dependencies, context)
                 : new ErrorNode(val, "ContainerFillComponent prototypes must be a sequence/list");
 
-            mapping.Add(keyVal, listVal);
+            mapping.Add(new ValidatedValueNode(node.GetKeyNode(key)), listVal);
         }
 
         return new ValidatedMappingNode(mapping);