Dungeon generation refactor (#17121)

Content.Shared/Procedural/PostGeneration/EntranceFlankPostGen.cs

@@ -0,0 +1,16 @@
+using Content.Shared.Maps;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom.Prototype;
+
+namespace Content.Shared.Procedural.PostGeneration;
+
+/// <summary>
+/// Spawns entities on either side of an entrance.
+/// </summary>
+public sealed class EntranceFlankPostGen : IPostDunGen
+{
+    [DataField("tile", customTypeSerializer:typeof(PrototypeIdSerializer<ContentTileDefinition>))]
+    public string Tile = "FloorSteel";
+
+    [DataField("entities")]
+    public List<string?> Entities = new();
+}