simplifying a function

Dramatic simplification of legacy code by separating code and data and applying some later C++.
Function removed from Application.cpp as it was in a anonymous namespace and could not easily be subjected to unit testing.
Added ProgramOptionsUtilities.h

src/App/ProgramOptionsUtilities.h

@@ -0,0 +1,81 @@
+/***************************************************************************
+*   Copyright (c) 2002 Jürgen Riegel <juergen.riegel@web.de>              *
+*                                                                         *
+*   This file is part of the FreeCAD CAx development system.              *
+*                                                                         *
+*   This program is free software; you can redistribute it and/or modify  *
+*   it under the terms of the GNU Library General Public License (LGPL)   *
+*   as published by the Free Software Foundation; either version 2 of     *
+*   the License, or (at your option) any later version.                   *
+*   for detail see the LICENCE text file.                                 *
+*                                                                         *
+*   FreeCAD 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 Library General Public License for more details.                  *
+*                                                                         *
+*   You should have received a copy of the GNU Library General Public     *
+*   License along with FreeCAD; if not, write to the Free Software        *
+*   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  *
+*   USA                                                                   *
+*                                                                         *
+***************************************************************************/
+
+#ifndef PROGRAMOPTIONSUTILITIES_H
+#define PROGRAMOPTIONSUTILITIES_H
+
+#include <string>
+
+namespace App::Util{
+
+std::pair<std::string, std::string> customSyntax(std::string_view strIn)
+{
+    if(strIn.size() < 2) {
+        return{};
+    }
+
+    char leadChr {strIn[0]};
+    std::string rest {strIn.substr(1)};
+
+    if (leadChr == '@') {
+        return {"response-file", rest};
+    }
+
+    if (leadChr != '-') {
+        return {};
+    }
+
+#if defined(FC_OS_MACOSX)
+    if (rest.find("psn_") == 0) {
+        return {"psn", rest.substr(4)};
+    }
+#endif
+
+    if(rest == "widgetcount"){
+        return {rest, ""};
+    }
+
+    constexpr std::array knowns {"display",
+                                 "style",
+                                 "graphicssystem",
+                                 "geometry",
+                                 "font",
+                                 "fn",
+                                 "background",
+                                 "bg",
+                                 "foreground",
+                                 "fg",
+                                 "button",
+                                 "btn",
+                                 "name",
+                                 "title",
+                                 "visual"};
+
+    if(std::find(knowns.begin(), knowns.end(), rest) != knowns.end()) {
+        return {rest, "null"};
+    }
+    return {};
+}
+
+} // namespace
+#endif// PROGRAMOPTIONSUTILITIES_H