Add PrepareAnvilEvent.

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/event/inventory/PrepareAnvilEvent.java

@@ -0,0 +1,47 @@
+package org.bukkit.event.inventory;
+
+import org.bukkit.event.HandlerList;
+import org.bukkit.inventory.AnvilInventory;
+import org.bukkit.inventory.InventoryView;
+import org.bukkit.inventory.ItemStack;
+
+/**
+ * Called when an item is put in a slot for repair by an anvil.
+ */
+public class PrepareAnvilEvent extends InventoryEvent {
+
+    private static final HandlerList handlers = new HandlerList();
+    private ItemStack result;
+
+    public PrepareAnvilEvent(InventoryView inventory, ItemStack result) {
+        super(inventory);
+        this.result = result;
+    }
+
+    @Override
+    public AnvilInventory getInventory() {
+        return (AnvilInventory) super.getInventory();
+    }
+
+    /**
+     * Get result item, may be null.
+     *
+     * @return result item
+     */
+    public ItemStack getResult() {
+        return result;
+    }
+
+    public void setResult(ItemStack result) {
+        this.result = result;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+}