Zombie Horse (and Drowned Horse) Implementation in Survival

Behavior:
- Can be ridden underwater.
- Burns in sunlight unless wearing horse armor, similar to zombies burning in sunlight without helmets. (Leather horse armor can be crafted, so the severity of potentially losing zombie horses is player controlled.) Seeks shelter from the sun in shade/water.
- Seeks out & attacks horses, with a guaranteed chance to zombify them. This ensures you're much less likely to lose your horses while also providing a renewable method.
- Turns into a drowned horse after 300 seconds submerged in water. The drowned horse allows vertical & stationary riding underwater, similar to creative flight.
- Zombie & drowned horses can be cured.

Obtaining:
1. In abandoned villages, in both stables & corrals, zombie horses spawn in place of horses. This gives abandoned villages a purpose, rewarding players with a unique mob. To keep them from burning in sunlight, if spawned in an open air corral, they could spawn with leather horse armor dyed to the color of the village type. For example, plains: white/yellow.

2. When lightning strikes a horse, they turn into a zombie horse, retaining stats & gear. This follows the lightning precedent of transformation, especially similar to pigs.

3. Breeding a horse & skeleton horse spawns a baby zombie horse, giving a renewable method & more uses to skeleton horse. The baby zombie horse wouldn't attack the parent until it grows up, but would be hostile to other horses.

Skeleton horses stay unique because of their sun immunity.