Stem: implement facing property

fixes #5858

technically speaking, the sideways states for non-fully-grown stems shouldn't exist, but they do in Bedrock, and changing this code to split non-fully-grown stems from fully grown ones would likely require BC breaks.
This was the minimum necessary to achieve the desired functionality.

src/block/Stem.php

@@ -23,6 +23,7 @@ declare(strict_types=1);
 
 namespace pocketmine\block;
 
+use pocketmine\data\runtime\RuntimeDataDescriber;
 use pocketmine\event\block\BlockGrowEvent;
 use pocketmine\item\Item;
 use pocketmine\math\Facing;
@@ -30,11 +31,34 @@ use function array_rand;
 use function mt_rand;
 
 abstract class Stem extends Crops{
+	protected int $facing = Facing::UP;
+
+	protected function describeBlockOnlyState(RuntimeDataDescriber $w) : void{
+		parent::describeBlockOnlyState($w);
+		$w->facingExcept($this->facing, Facing::DOWN);
+	}
+
+	public function getFacing() : int{ return $this->facing; }
+
+	/** @return $this */
+	public function setFacing(int $facing) : self{
+		if($facing === Facing::DOWN){
+			throw new \InvalidArgumentException("DOWN is not a valid facing for this block");
+		}
+		$this->facing = $facing;
+		return $this;
+	}
 
 	abstract protected function getPlant() : Block;
 
+	public function onNearbyBlockChange() : void{
+		if($this->facing !== Facing::UP && !$this->getSide($this->facing)->hasSameTypeId($this->getPlant())){
+			$this->position->getWorld()->setBlock($this->position, $this->setFacing(Facing::UP));
+		}
+	}
+
 	public function onRandomTick() : void{
-		if(mt_rand(0, 2) === 1){
+		if($this->facing === Facing::UP && mt_rand(0, 2) === 1){
 			$world = $this->position->getWorld();
 			if($this->age < self::MAX_AGE){
 				$block = clone $this;
@@ -52,11 +76,13 @@ abstract class Stem extends Crops{
 					}
 				}
 
-				$side = $this->getSide(Facing::HORIZONTAL[array_rand(Facing::HORIZONTAL)]);
+				$facing = Facing::HORIZONTAL[array_rand(Facing::HORIZONTAL)];
+				$side = $this->getSide($facing);
 				if($side->getTypeId() === BlockTypeIds::AIR && $side->getSide(Facing::DOWN)->hasTypeTag(BlockTypeTags::DIRT)){
 					$ev = new BlockGrowEvent($side, $grow);
 					$ev->call();
 					if(!$ev->isCancelled()){
+						$world->setBlock($this->position, $this->setFacing($facing));
 						$world->setBlock($side->position, $ev->getNewState());
 					}
 				}

src/data/bedrock/block/convert/BlockStateDeserializerHelper.php

@@ -236,9 +236,12 @@ final class BlockStateDeserializerHelper{
 
 	/** @throws BlockStateDeserializeException */
 	public static function decodeStem(Stem $block, BlockStateReader $in) : Stem{
-		//TODO: our stems don't support facings yet (facing_direction)
+		//In PM, we use Facing::UP to indicate that the stem is not attached to a pumpkin/melon, since this makes the
-		$in->todo(BlockStateNames::FACING_DIRECTION);
+		//most intuitive sense (the stem is pointing at the sky). However, Bedrock uses the DOWN state for this, which
-		return self::decodeCrops($block, $in);
+		//is absurd, and I refuse to make our API similarly absurd.
+		$facing = $in->readFacingWithoutUp();
+		return self::decodeCrops($block, $in)
+			->setFacing($facing === Facing::DOWN ? Facing::UP : $facing);
 	}
 
 	/** @throws BlockStateDeserializeException */

src/data/bedrock/block/convert/BlockStateSerializerHelper.php

@@ -223,8 +223,12 @@ final class BlockStateSerializerHelper{
 	}
 
 	public static function encodeStem(Stem $block, BlockStateWriter $out) : BlockStateWriter{
+		//In PM, we use Facing::UP to indicate that the stem is not attached to a pumpkin/melon, since this makes the
+		//most intuitive sense (the stem is pointing at the sky). However, Bedrock uses the DOWN state for this, which
+		//is absurd, and I refuse to make our API similarly absurd.
+		$facing = $block->getFacing();
 		return self::encodeCrops($block, $out)
-			->writeHorizontalFacing(Facing::NORTH); //TODO: PM impl doesn't support this yet
+			->writeFacingWithoutUp($facing === Facing::UP ? Facing::DOWN : $facing);
 	}
 
 	public static function encodeStone(string $type) : BlockStateWriter{