SPIGOT-436: Add accompanying getSpectatorTarget().

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/entity/Player.java

@@ -1037,6 +1037,15 @@ public interface Player extends HumanEntity, Conversable, CommandSender, Offline
      */
     public double getHealthScale();
 
+    /**
+     * Gets the entity which is followed by the camera when in
+     * {@link GameMode#SPECTATOR}.
+     *
+     * @return the followed entity, or null if not in spectator mode or not
+     * following a specific entity.
+     */
+    public Entity getSpectatorTarget();
+
     /**
      * Sets the entity which is followed by the camera when in
      * {@link GameMode#SPECTATOR}.