World: added setDisplayName()

this is an obvious use case, and I'm not really sure why it wasn't supported sooner.

src/event/world/WorldDisplayNameChangeEvent.php

@@ -0,0 +1,48 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+ */
+
+declare(strict_types=1);
+
+namespace pocketmine\event\world;
+
+use pocketmine\world\World;
+
+/**
+ * Called when a world's display name is changed.
+ */
+final class WorldDisplayNameChangeEvent extends WorldEvent{
+
+	public function __construct(
+		World $world,
+		private string $oldName,
+		private string $newName
+	){
+		parent::__construct($world);
+	}
+
+	public function getOldName() : string{
+		return $this->oldName;
+	}
+
+	public function getNewName() : string{
+		return $this->newName;
+	}
+}

src/world/World.php

@@ -51,6 +51,7 @@ use pocketmine\event\world\ChunkLoadEvent;
 use pocketmine\event\world\ChunkPopulateEvent;
 use pocketmine\event\world\ChunkUnloadEvent;
 use pocketmine\event\world\SpawnChangeEvent;
+use pocketmine\event\world\WorldDisplayNameChangeEvent;
 use pocketmine\event\world\WorldParticleEvent;
 use pocketmine\event\world\WorldSaveEvent;
 use pocketmine\event\world\WorldSoundEvent;
@@ -2971,6 +2972,16 @@ class World implements ChunkManager{
 		return $this->displayName;
 	}
 
+	/**
+	 * Sets the World display name.
+	 */
+	public function setDisplayName(string $name) : void{
+		(new WorldDisplayNameChangeEvent($this, $this->displayName, $name))->call();
+
+		$this->displayName = $name;
+		$this->provider->getWorldData()->setName($name);
+	}
+
 	/**
 	 * Returns the World folder name. This will not change at runtime and will be unique to a world per runtime.
 	 */

src/world/format/io/WorldData.php

@@ -34,6 +34,8 @@ interface WorldData{
 
 	public function getName() : string;
 
+	public function setName(string $value) : void;
+
 	/**
 	 * Returns the generator name
 	 */

src/world/format/io/data/BaseNbtWorldData.php

@@ -116,6 +116,10 @@ abstract class BaseNbtWorldData implements WorldData{
 		return $this->compoundTag->getString(self::TAG_LEVEL_NAME);
 	}
 
+	public function setName(string $value) : void{
+		$this->compoundTag->setString(self::TAG_LEVEL_NAME, $value);
+	}
+
 	public function getGenerator() : string{
 		return $this->compoundTag->getString(self::TAG_GENERATOR_NAME, "DEFAULT");
 	}