SPIGOT-4802: Add CrossbowMeta

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

paper-api/src/main/java/org/bukkit/inventory/meta/CrossbowMeta.java

@@ -0,0 +1,43 @@
+package org.bukkit.inventory.meta;
+
+import java.util.List;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public interface CrossbowMeta extends ItemMeta {
+
+    /**
+     * Returns whether the item has any charged projectiles.
+     *
+     * @return whether charged projectiles are present
+     */
+    boolean hasChargedProjectiles();
+
+    /**
+     * Returns an immutable list of the projectiles charged on this item.
+     *
+     * @return charged projectiles
+     */
+    @NotNull
+    List<ItemStack> getChargedProjectiles();
+
+    /**
+     * Sets the projectiles charged on this item.
+     *
+     * Removes all projectiles when given null.
+     *
+     * @param projectiles
+     * @throws IllegalArgumentException if one of the projectiles is not an
+     * arrow
+     */
+    void setChargedProjectiles(@Nullable List<ItemStack> projectiles);
+
+    /**
+     * Adds a charged projectile to this item.
+     *
+     * @param item projectile
+     * @throws IllegalArgumentException if the projectile is not an arrow
+     */
+    void addChargedProjectile(@NotNull ItemStack item);
+}