Improve the path select GUI (#5852)

- Allow lua to chose whatever directories or files can be selected
- Fix selecting directories
- Rename dialog to `guiPathSelectMenu` from `guiFileSelectMenu`
- Rename lua function for opening the menu from `show_file_open_dialog` to `show_path_select_dialog`
- Remove duplicate code and fix code style.

Related changes
- fix `clang-format` whitelist.
- Regenerate minetest.conf.example

src/guiPathSelectMenu.h

@@ -0,0 +1,62 @@
+/*
+ Minetest
+ Copyright (C) 2013 sapier
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License along
+ with this program; if not, write to the Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef GUIFILESELECTMENU_H_
+#define GUIFILESELECTMENU_H_
+
+#include <string>
+
+#include "modalMenu.h"
+#include "IGUIFileOpenDialog.h"
+#include "guiFormSpecMenu.h" //required because of TextDest only !!!
+
+class GUIFileSelectMenu : public GUIModalMenu
+{
+public:
+	GUIFileSelectMenu(gui::IGUIEnvironment *env, gui::IGUIElement *parent, s32 id,
+			IMenuManager *menumgr, const std::string &title,
+			const std::string &formid, bool is_file_select);
+	~GUIFileSelectMenu();
+
+	/*
+	 Remove and re-add (or reposition) stuff
+	 */
+	void regenerateGui(v2u32 screensize);
+
+	void drawMenu();
+
+	bool OnEvent(const SEvent &event);
+
+	void setTextDest(TextDest *dest) { m_text_dst = dest; }
+
+private:
+	void acceptInput();
+
+	std::wstring m_title;
+	bool m_accepted;
+
+	gui::IGUIFileOpenDialog *m_fileOpenDialog;
+
+	TextDest *m_text_dst;
+
+	std::string m_formname;
+	bool m_file_select_dialog;
+};
+
+#endif /* GUIFILESELECTMENU_H_ */