Use new `sendEquipmentChange` for `resetEquipment`
`resetEquipment` was previsouly using NMS because you'd have to send every change individually if you used the API, but now that Spigot added a new `Player#sendEquipmentChange` that takes a map, it can be sent all at once using API.
Also removed the `default -> UnsupportedOperationException` from methods that were implemented on all supported versions. (commit: 32cb5aa)
