Add ItemStack#displayName to get the formatted display name of an ItemStack (#5628)

The display name includes formatting such as item hover event, display name (in italics if renamed in anvil), and color based on rarity.

This is what vanilla uses for give command feedback, and when an item is shown in a death message.

Spigot-API-Patches/Adventure.patch

@@ -2869,6 +2869,15 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +     */
 +    @NotNull
 +    net.kyori.adventure.text.event.HoverEvent<net.kyori.adventure.text.event.HoverEvent.ShowItem> asHoverEvent(final @NotNull ItemStack item, final @NotNull java.util.function.UnaryOperator<net.kyori.adventure.text.event.HoverEvent.ShowItem> op);
++
++    /**
++     * Get the formatted display name of the {@link ItemStack}.
++     *
++     * @param itemStack the {@link ItemStack}
++     * @return display name of the {@link ItemStack}
++     */
++    @NotNull
++    net.kyori.adventure.text.Component displayName(@NotNull ItemStack itemStack);
 +    // Paper end
  }
 diff --git a/src/main/java/org/bukkit/inventory/ItemStack.java b/src/main/java/org/bukkit/inventory/ItemStack.java
@@ -2895,6 +2904,15 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    public net.kyori.adventure.text.event.HoverEvent<net.kyori.adventure.text.event.HoverEvent.ShowItem> asHoverEvent(final @NotNull java.util.function.UnaryOperator<net.kyori.adventure.text.event.HoverEvent.ShowItem> op) {
 +        return org.bukkit.Bukkit.getServer().getItemFactory().asHoverEvent(this, op);
 +    }
++
++    /**
++     * Get the formatted display name of the {@link ItemStack}.
++     *
++     * @return display name of the {@link ItemStack}
++     */
++    public @NotNull net.kyori.adventure.text.Component displayName() {
++        return Bukkit.getServer().getItemFactory().displayName(this);
++    }
 +    // Paper end
  }
 diff --git a/src/main/java/org/bukkit/inventory/meta/BookMeta.java b/src/main/java/org/bukkit/inventory/meta/BookMeta.java