Add button_url[] and hypertext element to allow mods to open web pages (#13825)

Fixes #12500

src/gui/guiOpenURL.h

@@ -0,0 +1,50 @@
+/*
+Part of Minetest
+Copyright (C) 2023 rubenwardy
+
+Permission to use, copy, modify, and distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#pragma once
+
+#include "irrlichttypes_extrabloated.h"
+#include "modalMenu.h"
+#include <string>
+
+class Client;
+class ISimpleTextureSource;
+
+class GUIOpenURLMenu : public GUIModalMenu
+{
+public:
+	GUIOpenURLMenu(gui::IGUIEnvironment *env, gui::IGUIElement *parent, s32 id,
+			IMenuManager *menumgr,
+			ISimpleTextureSource *tsrc, const std::string &url);
+
+	/*
+		Remove and re-add (or reposition) stuff
+	*/
+	void regenerateGui(v2u32 screensize);
+
+	void drawMenu();
+
+	bool OnEvent(const SEvent &event);
+
+protected:
+	std::wstring getLabelByID(s32 id) { return L""; }
+	std::string getNameByID(s32 id) { return ""; }
+
+private:
+	ISimpleTextureSource *m_tsrc;
+	std::string url;
+};