Player: Clean up item frame drop-item hack

This is now re-routed through a newly-created attack-block handler.
Closes #339

src/pocketmine/block/Block.php

@@ -380,6 +380,20 @@ class Block extends Position implements BlockIds, Metadatable{
 		return false;
 	}
 
+	/**
+	 * Called when this block is attacked (left-clicked). This is called when a player left-clicks the block to try and
+	 * start to break it in survival mode.
+	 *
+	 * @param Item        $item
+	 * @param int         $face
+	 * @param Player|null $player
+	 *
+	 * @return bool if an action took place, prevents starting to break the block if true.
+	 */
+	public function onAttack(Item $item, int $face, ?Player $player = null) : bool{
+		return false;
+	}
+
 	/**
 	 * Returns a base value used to compute block break times.
 	 * @return float

src/pocketmine/block/ItemFrame.php

@@ -156,6 +156,18 @@ class ItemFrame extends Flowable{
 		return true;
 	}
 
+	public function onAttack(Item $item, int $face, ?Player $player = null) : bool{
+		if($this->framedItem === null){
+			return false;
+		}
+		if(lcg_value() <= $this->itemDropChance){
+			$this->level->dropItem($this->add(0.5, 0.5, 0.5), $this->getFramedItem());
+		}
+		$this->setFramedItem(null);
+		$this->level->setBlock($this, $this);
+		return true;
+	}
+
 	public function onNearbyBlockChange() : void{
 		if(!$this->getSide(Facing::opposite($this->facing))->isSolid()){
 			$this->level->useBreakOn($this);