`conversion_duration` property on Zombies and Zombie Villagers (#2302)
* `conversion_duration` property
* these tags aren't static
* deprecate `drowned_conversion_duration`
* seconds -> ticks
* prevent exceptions by checking if entity is converting
* remove redundant method
* exclude PigZombies
* remove redundant tags arr
* prevent exceptions in property string
(
commit: 689ef23)
