Fixes and additions to the spawn reason API

Expose an entities spawn reason on the entity.
Pre existing entities will return NATURAL if it was a non
persistenting Living Entity, SPAWNER for spawners,
or DEFAULT since data was not stored.

Additionally, add missing spawn reasons.

Co-authored-by: Jake Potrebic <jake.m.potrebic@gmail.com>
Co-authored-by: Doc <nachito94@msn.com>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java

@@ -1014,4 +1014,11 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
         return this.getHandle().spawnedViaMobSpawner;
     }
     // Paper end - Entity#fromMobSpawner
+
+    // Paper start - entity spawn reason API
+    @Override
+    public org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason getEntitySpawnReason() {
+        return getHandle().spawnReason;
+    }
+    // Paper end - entity spawn reason API
 }