Add API for dealing with player UUIDs. Adds BUKKIT-5071, BUKKIT-5501

By: Travis Watkins <amaranth@ubuntu.com>

paper-api/src/main/java/org/bukkit/OfflinePlayer.java

@@ -1,6 +1,7 @@
 package org.bukkit;
 
 import java.util.Date;
+import java.util.UUID;
 
 import org.bukkit.configuration.serialization.ConfigurationSerializable;
 import org.bukkit.entity.AnimalTamer;
@@ -19,10 +20,20 @@ public interface OfflinePlayer extends ServerOperator, AnimalTamer, Configuratio
     /**
      * Returns the name of this player
      *
+     * @deprecated Use {@link #getUniqueId()} as player names are no longer
+     *     guaranteed to be unique
      * @return Player name
      */
+    @Deprecated
     public String getName();
 
+    /**
+     * Returns the UUID of this player
+     *
+     * @return Player UUID
+     */
+    public UUID getUniqueId();
+
     /**
      * Checks if this player is banned or not
      *