WI #2306 Protect against NullReferenceException when reading NameLiteral property

[fm-117]

Fixes #2306

The NullReferenceException regularly observed in the AddError method when checking REDEFINES may be caused by:

• either the NameLiteral being null
• or the Token of the NameLiteral being null.

This PR aims at fixing unsafe uses of SymbolInformation.NameLiteral.

[efr15]

This code is repeated 3 times.
It could be factorized in a methode AddToSymbolInformation with this code:

        private void AddToSymbolInformation(SymbolDefinition specialRegisterName, SymbolReference specialRegisterReference)
        {
            var specialRegisterNameToken = specialRegisterName?.NameLiteral?.Token;
            if (specialRegisterNameToken != null)
            {
                CobolWordsBuilder.symbolInformationForTokens[specialRegisterNameToken] = specialRegisterName;
            }

            var specialRegisterReferenceToken = specialRegisterReference?.NameLiteral?.Token;
            if (specialRegisterReferenceToken != null)
            {
                CobolWordsBuilder.symbolInformationForTokens[specialRegisterReferenceToken] = specialRegisterReference;
            }
        }

Calll it like this;
AddToSymbolInformation(specialRegister.DataDescriptionEntry?.DataName, specialRegister.SymbolReference);

[efr15]

This code is repeated 4 times. Similar factorization with method:

        private void AddToSymbolInformation(SymbolReference reference)
        {
            var token = reference.NameLiteral?.Token;
            if (token != null)
            {
                symbolInformationForTokens[token] = reference;
            }
        }