SPIGOT-6888: Add SpawnReason for Vex spawned by Evokers

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

@@ -177,6 +177,10 @@ public class CreatureSpawnEvent extends EntitySpawnEvent {
          * When a piglin is converted to a zombified piglib.
          */
         PIGLIN_ZOMBIFIED,
+        /**
+         * When an entity is created by a cast spell.
+         */
+        SPELL,
         /**
          * When an entity is shaking in Powder Snow and a new entity spawns.
          */