SPIGOT-5802: Add SmithingRecipe API

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

paper-api/src/main/java/org/bukkit/inventory/SmithingRecipe.java

@@ -0,0 +1,63 @@
+package org.bukkit.inventory;
+
+import org.bukkit.Keyed;
+import org.bukkit.NamespacedKey;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Represents a smithing recipe.
+ */
+public class SmithingRecipe implements Recipe, Keyed {
+
+    private final NamespacedKey key;
+    private final ItemStack result;
+    private final RecipeChoice base;
+    private final RecipeChoice addition;
+
+    /**
+     * Create a smithing recipe to produce the specified result ItemStack.
+     *
+     * @param key The unique recipe key
+     * @param result The item you want the recipe to create.
+     * @param base The base ingredient
+     * @param addition The addition ingredient
+     */
+    public SmithingRecipe(@NotNull NamespacedKey key, @NotNull ItemStack result, @NotNull RecipeChoice base, @NotNull RecipeChoice addition) {
+        this.key = key;
+        this.result = result;
+        this.base = base;
+        this.addition = addition;
+    }
+
+    /**
+     * Get the base recipe item.
+     *
+     * @return base choice
+     */
+    @NotNull
+    public RecipeChoice getBase() {
+        return base.clone();
+    }
+
+    /**
+     * Get the addition recipe item.
+     *
+     * @return addition choice
+     */
+    @NotNull
+    public RecipeChoice getAddition() {
+        return addition.clone();
+    }
+
+    @NotNull
+    @Override
+    public ItemStack getResult() {
+        return result.clone();
+    }
+
+    @NotNull
+    @Override
+    public NamespacedKey getKey() {
+        return this.key;
+    }
+}