Added AchievementsWindow QDialog

AchievementsWindow is the dialog box that will eventually contain the settings and progress data for RetroAchievements on Dolphin. This adds the barebones dialog, and connects it to MainWindow's MenuBar.

Source/Core/DolphinQt/Achievements/AchievementsWindow.h

@@ -0,0 +1,26 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#ifdef USE_RETRO_ACHIEVEMENTS
+#include <QDialog>
+
+class QDialogButtonBox;
+
+class AchievementsWindow : public QDialog
+{
+  Q_OBJECT
+public:
+  explicit AchievementsWindow(QWidget* parent);
+  void UpdateData();
+
+private:
+  void CreateMainLayout();
+  void showEvent(QShowEvent* event);
+  void ConnectWidgets();
+
+  QDialogButtonBox* m_button_box;
+};
+
+#endif  // USE_RETRO_ACHIEVEMENTS