Allow taking screenshots in main menu (#16749)

Co-authored-by: sfan5 <sfan5@live.de>
Co-authored-by: siliconsniffer <siliconsniffer@users.noreply.github.com>

src/util/screenshot.h

@@ -0,0 +1,20 @@
+// Luanti
+// SPDX-License-Identifier: LGPL-2.1-or-later
+// Copyright (C) 2013 celeron55, Perttu Ahola <celeron55@gmail.com>
+
+#pragma once
+
+#include <string>
+
+namespace video {
+	class IVideoDriver;
+}
+
+/**
+ * Take a screenshot and save it to disk
+ * @param driver Video driver to use for the screenshot
+ * @param filename_out Output parameter that receives the path to the saved screenshot
+ * @return true if the screenshot was saved successfully, false otherwise
+ */
+bool takeScreenshot(video::IVideoDriver *driver, std::string &filename_out);
+