Server: added getPlayerByUUID() and getPlayerByRawUUID()

closes #2047

Since the player list already indexes players by UUID, it's simple to just use that for fetching the player.

A possible future improvement could be to allow fetching an _offline_ player by UUID, but no capability to do that is yet available.

src/pocketmine/Server.php

@@ -878,6 +878,28 @@ class Server{
 		return $matchedPlayers;
 	}
 
+	/**
+	 * Returns the player online with the specified raw UUID, or null if not found
+	 *
+	 * @param string $rawUUID
+	 *
+	 * @return null|Player
+	 */
+	public function getPlayerByRawUUID(string $rawUUID) : ?Player{
+		return $this->playerList[$rawUUID] ?? null;
+	}
+
+	/**
+	 * Returns the player online with a UUID equivalent to the specified UUID object, or null if not found
+	 *
+	 * @param UUID $uuid
+	 *
+	 * @return null|Player
+	 */
+	public function getPlayerByUUID(UUID $uuid) : ?Player{
+		return $this->getPlayerByRawUUID($uuid->toBinary());
+	}
+
 	/**
 	 * @return Level[]
 	 */