Add layers field to construction prototype (#14222)

Content.Shared/Construction/Prototypes/ConstructionPrototype.cs

@@ -46,6 +46,12 @@ namespace Content.Shared.Construction.Prototypes
         [DataField("icon")]
         public SpriteSpecifier Icon { get; } = SpriteSpecifier.Invalid;
 
+        /// <summary>
+        ///     Texture paths used for the construction ghost.
+        /// </summary>
+        [DataField("layers")]
+        private List<SpriteSpecifier>? _layers;
+
         /// <summary>
         ///     If you can start building or complete steps on impassable terrain.
         /// </summary>
@@ -70,6 +76,7 @@ namespace Content.Shared.Construction.Prototypes
         public bool CanRotate { get; } = true;
 
         public IReadOnlyList<IConstructionCondition> Conditions => _conditions;
+        public IReadOnlyList<SpriteSpecifier> Layers => _layers ?? new List<SpriteSpecifier>{Icon};
     }
 
     public enum ConstructionType