SPIGOT-7857: Improve ItemMeta block data deserialization

By: blablubbabc <lukas@wirsindwir.de>

paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaItem.java

@@ -519,10 +519,17 @@ class CraftMetaItem implements ItemMeta, Damageable, Repairable, BlockDataMeta {
         if (blockData != null) {
             Map<String, String> mapBlockData = new HashMap<>();
 
+            if (blockData instanceof Map) {
+                for (Entry<?, ?> entry : ((Map<?, ?>) blockData).entrySet()) {
+                    mapBlockData.put(entry.getKey().toString(), entry.getValue().toString());
+                }
+            } else {
+                // Legacy pre 1.20.5:
                 NBTTagCompound nbtBlockData = (NBTTagCompound) CraftNBTTagConfigSerializer.deserialize(blockData);
                 for (String key : nbtBlockData.getAllKeys()) {
                     mapBlockData.put(key, nbtBlockData.getString(key));
                 }
+            }
 
             this.blockData = mapBlockData;
         }