qt: implement RequestExit for applets

src/core/frontend/applets/applet.h

@@ -0,0 +1,14 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+namespace Core::Frontend {
+
+class Applet {
+public:
+    virtual ~Applet() = default;
+    virtual void Close() const = 0;
+};
+
+} // namespace Core::Frontend