Add SpawnReason.SHEARING

By: klugemonkey <klugemonkey@spawnchunk.com>

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

@@ -173,6 +173,10 @@ public class CreatureSpawnEvent extends EntityEvent implements Cancellable {
          * When a creature is spawned by another entity drowning
          */
         DROWNED,
+        /**
+         * When an cow is spawned by shearing a mushroom cow
+         */
+        SHEARED,
         /**
          * When a creature is spawned by plugins
          */