SPIGOT-7204: Add TeleportCause#DISMOUNT

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

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

@@ -73,6 +73,10 @@ public class PlayerTeleportEvent extends PlayerMoveEvent {
          * fruit
          */
         CHORUS_FRUIT,
+        /**
+         * Indicates the teleportation was caused by a player exiting a vehicle
+         */
+        DISMOUNT,
         /**
          * Indicates the teleportation was caused by an event not covered by
          * this enum