Add Mellohi to Woodland Mansion chests

The Music Disc "mellohi" should be added to the loot table for chests in the Woodland Mansion structure. Mellohi is a sinister, dismal-sounding track that fits perfectly with the Illagers' aesthetic, so it only makes sense that it would be in their possession. Its chance of generating could take a cut from 13's and cat's chances, giving all three music discs a roughly 14.53% chance to spawn. Alternatively, mellohi could generate instead of the other two music discs, which would make the Woodland Mansion's loot stand out a bit more from other structures' loot tables.