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

this allows cleaning up a whole lot of abusable mess from the API, and we never properly supported overriding built-in block types anyway.

src/block/BambooSapling.php

@@ -36,7 +36,7 @@ use pocketmine\world\BlockTransaction;
 final class BambooSapling extends Flowable{
 	private bool $ready = false;
 
-	protected function describeState(RuntimeDataDescriber $w) : void{
+	public function describeState(RuntimeDataDescriber $w) : void{
 		$w->bool($this->ready);
 	}