Optimize map edits by skipping expensive tile index property copies

Author: SinZ163

src/SMAPI/Framework/Content/AssetDataForMap.cs

@@ -8,6 +8,7 @@
 using xTile;
 using xTile.Dimensions;
 using xTile.Layers;
+using xTile.ObjectModel;
 using xTile.Tiles;
 using Rectangle = Microsoft.Xna.Framework.Rectangle;
 
@@ -90,8 +91,7 @@ public void PatchMap(Map source, Rectangle? sourceArea = null, Rectangle? target
 
                 // add tilesheet
                 targetSheet = new TileSheet(id, target, sourceSheet.ImageSource, sourceSheet.SheetSize, sourceSheet.TileSize);
-                for (int i = 0, tileCount = sourceSheet.TileCount; i < tileCount; ++i)
-                    targetSheet.TileIndexProperties[i].CopyFrom(sourceSheet.TileIndexProperties[i]);
+                this.Reflection.GetField<PropertyCollection>(targetSheet, "m_propertyCollection").SetValue((PropertyCollection)sourceSheet.Properties);
                 target.AddTileSheet(targetSheet);
             }