Revert "ItemBlock: drop the charade about overriding built-in block types"

This reverts commit f64dc01bd1.

I forgot that the ItemBlock constructor implicitly strips off any states
of the origin block, which is something that we unfortunately can't do
any other way right now, since the blocks don't remember their default
states.

src/block/Sponge.php

@@ -28,7 +28,7 @@ use pocketmine\data\runtime\RuntimeDataDescriber;
 class Sponge extends Opaque{
 	protected bool $wet = false;
 
-	public function describeType(RuntimeDataDescriber $w) : void{
+	protected function describeType(RuntimeDataDescriber $w) : void{
 		$w->bool($this->wet);
 	}