Absorb pocketmine/classloader into the core code

the only use for this class is to facilitate random runtime plugin loading, and it's not complete even for that purpose.

Since nothing but PM uses pocketmine/classloader anyway, it doesn't make sense to have it outside the core. As with LogPthreads, it's just adding more maintenance work.

src/plugin/PharPluginLoader.php

@@ -23,6 +23,7 @@ declare(strict_types=1);
 
 namespace pocketmine\plugin;
 
+use pocketmine\thread\ThreadSafeClassLoader;
 use function is_file;
 use function str_ends_with;
 
@@ -31,7 +32,7 @@ use function str_ends_with;
  */
 class PharPluginLoader implements PluginLoader{
 	public function __construct(
-		private \DynamicClassLoader $loader
+		private ThreadSafeClassLoader $loader
 	){}
 
 	public function canLoadPlugin(string $path) : bool{