fix: correctly (de)serialise ItemType (#2620)

- InternalId changes depending on ~~magic~~ so we should not store this value
 - fixes #2589

worldedit-core/src/main/java/com/sk89q/worldedit/util/gson/GsonUtil.java

@@ -23,6 +23,8 @@ import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.sk89q.worldedit.math.BlockVector3;
 import com.sk89q.worldedit.math.Vector3;
+import com.sk89q.worldedit.world.item.ItemType;
+import com.sk89q.worldedit.world.item.ItemTypes;
 
 /**
  * Utility methods for Google's GSON library.
@@ -41,6 +43,7 @@ public final class GsonUtil {
         GsonBuilder gsonBuilder = new GsonBuilder();
         gsonBuilder.registerTypeAdapter(Vector3.class, new VectorAdapter());
         gsonBuilder.registerTypeAdapter(BlockVector3.class, new BlockVectorAdapter());
+        gsonBuilder.registerTypeAdapter(ItemType.class, new ItemTypeAdapter());
         return gsonBuilder;
     }
 

worldedit-core/src/main/java/com/sk89q/worldedit/util/gson/ItemTypeAdapter.java

@@ -0,0 +1,26 @@
+package com.sk89q.worldedit.util.gson;
+
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import com.sk89q.worldedit.world.item.ItemType;
+import com.sk89q.worldedit.world.item.ItemTypes;
+
+import java.lang.reflect.Type;
+
+public final class ItemTypeAdapter implements JsonDeserializer<ItemType> {
+
+    @Override
+    public ItemType deserialize(JsonElement json, Type type, JsonDeserializationContext cont) throws JsonParseException {
+        JsonObject jsonObject = json.getAsJsonObject();
+        String id = jsonObject.get("id").getAsString();
+        ItemType itemType = ItemTypes.get(id);
+        if (itemType == null) {
+            throw new JsonParseException("Could not parse item type `" + id + "`");
+        }
+        return itemType;
+    }
+
+}

worldedit-core/src/main/java/com/sk89q/worldedit/world/item/ItemType.java

@@ -79,7 +79,7 @@ public class ItemType implements RegistryItem, Keyed {
     }
 
     //FAWE start
-    private int internalId;
+    private transient int internalId;
 
     @Override
     public void setInternalId(int internalId) {