Add missing zombie/skeleton counterparts

Most zombie and skeleton variants have counterparts with the most recent examples being the Parched (skeleton counterpart for the husk) and the Frostbite (zombie counterpart for the stray).

Some variants are still missing counterparts, though, so here they are with the unique names and traits they could have.

Wither Zombie (Wither Skeleton counterpart): Growing Decay - This is similar to the wither effect, but it takes away one more point of damage each time.

Sunken (Drowned counterpart): Prismarine arrows - These arrows fly like normal arrows when used underwater, similarly to tridents.

Skeletal Piglin (Zombified Piglin counterpart): Crossbows - Living piglins can spawn with swords or crossbows while zombified piglins can only spawn with swords. Skeletal piglins would therefor only spawn with crossbows.