Modernize lua read (part 2 & 3): C++ templating assurance (#7410)

* Modernize lua read (part 2 & 3): C++ templating assurance

Implement the boolean reader
Implement the string reader
Also remove unused & unimplemented script_error_handler
Add a reader with default value

src/script/common/helper.h

@@ -0,0 +1,54 @@
+/*
+Minetest
+Copyright (C) 2018 nerzhul, Loic Blot <loic.blot@unix-experience.fr>
+
+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.
+*/
+
+#pragma once
+
+extern "C" {
+#include <lua.h>
+#include <lauxlib.h>
+}
+
+class LuaHelper
+{
+protected:
+	static bool isNaN(lua_State *L, int idx);
+
+	/**
+	 * Read a value using a template type T from Lua State L and index
+	 *
+	 *
+	 * @tparam T type to read from Lua
+	 * @param L Lua state
+	 * @param index Lua Index to read
+	 * @return read value from Lua
+	 */
+	template <typename T> static T readParam(lua_State *L, int index);
+
+	/**
+	 * Read a value using a template type T from Lua State L and index
+	 *
+	 * @tparam T type to read from Lua
+	 * @param L Lua state
+	 * @param index Lua Index to read
+	 * @param default_value default value to apply if nil
+	 * @return read value from Lua or default value if nil
+	 */
+	template <typename T>
+	static T readParam(lua_State *L, int index, const T &default_value);
+};