Revert "Block: Get rid of state bitmasks"

This reverts commit b7b05e729e.

Apparently this was premature, because we still need these things to deal with default state remapping.

src/pocketmine/block/Stair.php

@@ -53,6 +53,10 @@ abstract class Stair extends Transparent{
 		$this->upsideDown = ($stateMeta & 0x04) !== 0;
 	}
 
+	public function getStateBitmask() : int{
+		return 0b111;
+	}
+
 	public function readStateFromWorld() : void{
 		parent::readStateFromWorld();