GUIInventoryList: Keep item size while moving (#12896)

src/gui/guiInventoryList.h

@@ -34,10 +34,12 @@ public:
 
 		ItemSpec(const InventoryLocation &a_inventoryloc,
 				const std::string &a_listname,
-				s32 a_i) :
+				s32 a_i,
+				const v2s32 slotsize) :
 			inventoryloc(a_inventoryloc),
 			listname(a_listname),
-			i(a_i)
+			i(a_i),
+			slotsize(slotsize)
 		{
 		}
 
@@ -46,6 +48,7 @@ public:
 		InventoryLocation inventoryloc;
 		std::string listname;
 		s32 i = -1;
+		v2s32 slotsize;
 	};
 
 	// options for inventorylists that are setable with the lua api
@@ -99,6 +102,11 @@ public:
 		m_options.slotbordercolor = slotbordercolor;
 	}
 
+	const v2s32 getSlotSize() const noexcept
+	{
+		return m_slot_size;
+	}
+
 	// returns -1 if not item is at pos p
 	s32 getItemIndexAtPos(v2s32 p) const;