Fix "Unregistered holder" exception when applying an ArchetypeVolume to a world

[AlexandreArcil]

Related to #4222

Bug

When a biome is applied through ArchetypeVolume, the exception "Unregistered holder in ResourceKey[minecraft:root / minecraft:worldgen/biome]: Direct{net.minecraft.world.level.biome.Biome@XXXXXXX};" is thrown when the chunk is saved.

Cause

The root error is the function Registry#safeCastToReference which check that the Holder is a Reference, which is not the case after an ArchetypeVolume is applied to a world as it sets biomes with a Holder.Direct.

Fix

Change the Holder.Direct to a Holder.Reference when a biome is set to a LevelChunkSection.

Reproduction

I used this code to create and apply an ArchetypeVolume:

private ArchetypeVolume volume;

@Listener
public void rightClick(InteractBlockEvent.Secondary event) {
    if(event.context().get(EventContextKeys.USED_HAND).orElse(HandTypes.OFF_HAND.get()).equals(HandTypes.MAIN_HAND.get())) {
        Vector3i pos = event.interactionPoint().toInt();
        ServerWorld serverWorld = Sponge.server().worldManager().world(event.block().world()).get();
        if (volume == null) {
            volume = serverWorld.createArchetypeVolume(pos, pos.add(0, 1, 0), pos);
            logger.info("volume created");
        } else {
            volume.applyToWorld(serverWorld, pos, SpawnTypes.PLUGIN);
            logger.info("volume applied");
            volume = null;
        }
    }
}