refactor(Core/Player): extract methods based on existing categories (#6838)

src/server/game/Entities/Player/TradeData.h

@@ -56,4 +56,4 @@ private:                                                // fields
     ObjectGuid m_spellCastItem;                         // applied spell casted by item use
 
     ObjectGuid m_items[TRADE_SLOT_COUNT];               // traded itmes from m_player side including non-traded slot
-};
+};