#855: Add HumanEntity#getItemInUse and Material#getSlipperiness

By: konsolas <vincentyntang@gmail.com>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftHumanEntity.java

@@ -450,6 +450,12 @@ public class CraftHumanEntity extends CraftLivingEntity implements HumanEntity {
         return getHandle().isHandRaised();
     }
 
+    @Override
+    public ItemStack getItemInUse() {
+        net.minecraft.world.item.ItemStack item = getHandle().getActiveItem();
+        return item.isEmpty() ? null : CraftItemStack.asCraftMirror(item);
+    }
+
     @Override
     public boolean setWindowProperty(InventoryView.Property prop, int value) {
         return false;