ItemBlock: reference blocks directly (take 2)

This was first attempted in f64dc01bd1, but reverted, since I hadn't considered how to handle stripping state data from blocks.

This removes the abusable API RuntimeBlockStateRegistry::fromTypeId() and related methods. These were only used to allow ItemBlocks to magically start referencing other blocks if the blocks were overridden by a plugin, but this was never a well-supported use-case anyway.

Instead of relying on RuntimeBlockStateRegistry, we remember the state that the block had during its constructor, and use that to normalize the non-item properties for asItem().

closes #5609

src/block/Sponge.php

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