MC-165184Arrows/firework rockets on a pillager's offhand can be consumed
Pillagers are able to actually consume arrows/firework rockets in their offhand items.
How to Reproduce
1. Run
/summon pillager ~ ~ ~ {HandItems:[{id:crossbow,Count:1b},{id:tipped_arrow,Count:1b,tag:{Potion:strong_regeneration}}]}
2.
/summon skeleton ~ ~ ~ {HandItems:[{id:bow,Count:1b},{id:tipped_arrow,Count:1b,tag:{Potion:strong_regeneration}}],ArmorItems:[{},{},{},{id:carved_pumpkin,Count:1b}]}
→ 
The regeneration tipped arrow disappears from the pillager's offhand.
This does not affect other arrow-shooting mobs.
