Implement cauldrons (#5163)

the following things are currently not implemented:

- particle/sound effects when an entity extinguishes itself
- particle/sound effects when mixing different stuff in a cauldron
- powder snow cauldron

both of these things are contingent on #5169, but for the time being, the PR is functionally complete and I want to move on to something else without being stalled by the particle+sound problem (which I haven't yet decided how to solve).

tests/phpunit/data/bedrock/block/convert/BlockSerializerDeserializerTest.php

@@ -27,6 +27,7 @@ use PHPUnit\Framework\TestCase;
 use pocketmine\block\BaseBanner;
 use pocketmine\block\Bed;
 use pocketmine\block\BlockFactory;
+use pocketmine\block\BlockTypeIds;
 use pocketmine\block\Skull;
 use pocketmine\data\bedrock\block\BlockStateDeserializeException;
 use pocketmine\data\bedrock\block\BlockStateSerializeException;
@@ -54,6 +55,11 @@ final class BlockSerializerDeserializerTest extends TestCase{
 				self::fail($e->getMessage());
 			}
 
+			if($block->getTypeId() === BlockTypeIds::POTION_CAULDRON){
+				//this pretends to be a water cauldron in the blockstate, and stores its actual data in the blockentity
+				continue;
+			}
+
 			//The following are workarounds for differences in blockstate representation in Bedrock vs PM
 			//In these cases, some properties are not stored in the blockstate (but rather in the block entity NBT), but
 			//they do form part of the internal blockstate hash in PM. This leads to inconsistencies when serializing