Improve the flexibility of WorldProvider registration

WorldProviders now have the following requirements removed:
- __construct() is no longer required to have a specific signature
- static isValid() no longer needs to be implemented (you will still need it for registering, but it can be declared anywhere now)
- static generate() no longer needs to be implemented

This paves the way for more interesting types of world providers that use something other than local disk to store chunks (e.g. a mysql database).

WorldProviderManager no longer accepts class-string<WorldProvider>. Instead, WorldProviderManagerEntry is required, with 2 or 3 callbacks:
- ReadOnlyWorldProviderManager must provide a callback for isValid, and a callback for fromPath
- WritableWorldProviderManagerEntry must provide the same, and also a generate() callback

In practice, this requires zero changes to the WorldProviders themselves, since a WorldProviderManagerEntry can be created like this:
`new WritableWorldProviderManagerEntry(\Closure::fromCallable([LevelDB::class, 'isValid']), fn(string ) => new LevelDB(), \Closure::fromCallable([LevelDB::class, 'generate']))`

This provides identical functionality to before for the provider itself; only registration is changed.

src/world/format/io/WorldProviderManagerEntry.php

@@ -0,0 +1,53 @@
+<?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\world\format\io;
+
+use pocketmine\world\format\io\exception\CorruptedWorldException;
+use pocketmine\world\format\io\exception\UnsupportedWorldFormatException;
+
+/**
+ * @phpstan-type IsValid \Closure(string $path) : bool
+ */
+abstract class WorldProviderManagerEntry{
+
+	/** @phpstan-var IsValid */
+	protected \Closure $isValid;
+
+	/** @phpstan-param IsValid $isValid */
+	protected function __construct(\Closure $isValid){
+		$this->isValid = $isValid;
+	}
+
+	/**
+	 * Tells if the path is a valid world.
+	 * This must tell if the current format supports opening the files in the directory
+	 */
+	public function isValid(string $path) : bool{ return ($this->isValid)($path); }
+
+	/**
+	 * @throws CorruptedWorldException
+	 * @throws UnsupportedWorldFormatException
+	 */
+	abstract public function fromPath(string $path) : WorldProvider;
+}