Added SpawnReason.BUILD_SNOWMAN.

By: EvilSeph <evilseph@gmail.com>

paper-api/src/main/java/org/bukkit/event/entity/CreatureSpawnEvent.java

@@ -100,6 +100,10 @@ public class CreatureSpawnEvent extends EntityEvent implements Cancellable {
          * When a creature is spawned by a player that is sleeping
          */
         BED,
+        /**
+         * When a snowman is spawned by being built
+         */
+        BUILD_SNOWMAN,
         /**
          * When a creature is manually spawned
          */