Custom Piglin Bartering

port 1.5.0 to 1.21-1.21.1

From 1.5.0: port 1.4.0 to 1.20.5-1.20.6

From 1.4.0:

• fixed #2: entire gold nugget stacks are taken for barter instead of just one
• made it so piglins won't drop non-gold barterable items in favor of gold items

A cumulative changelog can be found here