SPIGOT-7309: Add API for jukebox inventories

By: Parker Hawke <hawkeboyz2@hotmail.com>

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

@@ -0,0 +1,35 @@
+package org.bukkit.inventory;
+
+import org.bukkit.Tag;
+import org.bukkit.block.Jukebox;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * Interface to the inventory of a Jukebox.
+ */
+public interface JukeboxInventory extends Inventory {
+
+    /**
+     * Set the record in the jukebox.
+     * <p>
+     * This will immediately start playing the inserted item or stop playing if the
+     * item provided is null. If the provided item is not a record (according to
+     * {@link Tag#ITEMS_MUSIC_DISCS}), this method will do nothing and not set the
+     * item in the inventory.
+     *
+     * @param item the new record
+     */
+    void setRecord(@Nullable ItemStack item);
+
+    /**
+     * Get the record in the jukebox.
+     *
+     * @return the current record
+     */
+    @Nullable
+    ItemStack getRecord();
+
+    @Nullable
+    @Override
+    public Jukebox getHolder();
+}