Improve villager trading code

[DrexHD]

This PR improves the villager trading code by:

• Using vanilla's Trade Factories instead of reimplementing (access wideners)
• Using the random instance provided, instead of creating a new one
• Rework SellSandwichFactory to be compatible with my own mod VillagerFix

[FoundationGames]

Looks good so far, will be merged and tested for any necessary revisions. Thanks for contributing!