Update pack for 1.21.3

[Novelyst]

I've run Slicer on the pack to cover the 1.20.2 changes and the 1.20.5 changes and deleted the leftover files no longer in use. I've also:

• Moved the Alex and Steve skins to the entity\player folder introduced in 1.19.3 changes.
• Changed grass to short_grass following 1.20.3 changes and updated the according block states.
• Renamed the scute to turtle_scute following 1.20.5 changes.
• Moved player armour, horse armour, elytra, and llama decorations into the new entity\equipment folder following 1.21.2 changes.
• Deleted some empty particle files which 1.21.3 doesn't have, though the removal of which I can't pin down.
• Renamed the seemingly erroneously labelled darkoak in the entity\boat folder to dark_oak, removing the old one.