Add Raw Byte ItemStack Serialization

Serializes using NBT which is safer for server data migrations than bukkits format.

Co-authored-by: Nassim Jahnke <nassim@njahnke.dev>

paper-api/src/main/java/org/bukkit/UnsafeValues.java

@@ -164,5 +164,9 @@ public interface UnsafeValues {
     default com.destroystokyo.paper.util.VersionFetcher getVersionFetcher() {
         return new com.destroystokyo.paper.util.VersionFetcher.DummyVersionFetcher();
     }
+
+    byte[] serializeItem(ItemStack item);
+
+    ItemStack deserializeItem(byte[] data);
     // Paper end
 }