[Bleeding] Add SpawnReasons to cover new Minecraft features.

Adds BUKKIT-5370, BUKKIT-5378, BUKKIT-5382, BUKKIT-5482. Covers zombie
villagers, ocelot babies, silverfish popping out of blocks, and mobs
spawning with a mount.

src/main/java/org/bukkit/event/entity/CreatureSpawnEvent.java

@@ -162,6 +162,27 @@ public class CreatureSpawnEvent extends EntityEvent implements Cancellable {
          * When a creature is spawned by a dispenser dispensing an egg
          */
         DISPENSE_EGG,
+        /**
+         * When a zombie infects a villager
+         */
+        INFECTION,
+        /**
+         * When a villager is cured from infection
+         */
+        CURED,
+        /**
+         * When an ocelot has a baby spawned along with them
+         */
+        OCELOT_BABY,
+        /**
+         * When a silverfish spawns from a block
+         */
+        SILVERFISH_BLOCK,
+        /**
+         * When an entity spawns as a mount of another entity (mostly chicken
+         * jockeys)
+         */
+        MOUNT,
         /**
          * When a creature is spawned by plugins
          */