SPIGOT-362: Add TeleportCause.SPECTATE

By: Thinkofdeath <thinkofdeath@spigotmc.org>

paper-api/src/main/java/org/bukkit/event/player/PlayerTeleportEvent.java

@@ -55,6 +55,11 @@ public class PlayerTeleportEvent extends PlayerMoveEvent {
          * portal
          */
         END_PORTAL,
+        /**
+         * Indicates the teleportation was caused by a player teleporting to a
+         * Entity/Player via the specatator menu
+         */
+        SPECTATE,
         /**
          * Indicates the teleportation was caused by an event not covered by
          * this enum