Librarian Villager Rework

This is an alternative idea to the current villager rework snapshot. My idea would be to, instead of locking enchants based on villager type, just replace buying books with duplicating books, replacing the book in the trade with an enchanted book of the same type. Mending and Frost walker would also likely need a new way to obtain the first book, which could be loot from woodland mansions and igloos respectively.