Fix ore dropping and implement subfields

src/main/java/emu/grasscutter/data/server/SubfieldMapping.java

@@ -0,0 +1,15 @@
+package emu.grasscutter.data.server;
+
+import lombok.Data;
+
+@Data
+public class SubfieldMapping {
+    private int entityId;
+    private SubfieldMappingEntry[] subfields;
+
+    @Data
+    public class SubfieldMappingEntry {
+        private String subfieldName;
+        private int drop_id;
+    }
+}