add Shulker Sorting

[aria1th]

This will allow accessing Inventory inside shulkers and sort based on it. Order : Shulker item first -> inventory (optional) next, based on Slots

[manuelgrabowski]

@kyrptonaught Do you think you'll want to merge this? I came here to open an issue asking for Shulker box support, but found that this MR already exists. It's the only thing this mod is missing for me to be the perfect sorting mod, would love if this could be added.