Add confirmation dialog when about to discard a playlist

The confirmation will only show if items have been added to the
playlist.

Closes https://github.com/ppy/osu/issues/19444.

osu.Game/Screens/Menu/ConfirmDiscardChangesDialog.cs

@@ -0,0 +1,39 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using osu.Framework.Graphics.Sprites;
+using osu.Game.Overlays.Dialog;
+
+namespace osu.Game.Screens.Menu
+{
+    public class ConfirmDiscardChangesDialog : PopupDialog
+    {
+        /// <summary>
+        /// Construct a new discard changes confirmation dialog.
+        /// </summary>
+        /// <param name="onConfirm">An action to perform on confirmation.</param>
+        /// <param name="onCancel">An optional action to perform on cancel.</param>
+        public ConfirmDiscardChangesDialog(Action onConfirm, Action? onCancel = null)
+        {
+            HeaderText = "Are you sure you want to go back?";
+            BodyText = "This will discard any unsaved changes";
+
+            Icon = FontAwesome.Solid.ExclamationTriangle;
+
+            Buttons = new PopupDialogButton[]
+            {
+                new PopupDialogDangerousButton
+                {
+                    Text = @"Yes",
+                    Action = onConfirm
+                },
+                new PopupDialogCancelButton
+                {
+                    Text = @"No I didn't mean to",
+                    Action = onCancel
+                },
+            };
+        }
+    }
+}