Fix #420 - Check for value token before expanding enumerable types with separator char

[wo-roberts]

No description provided.

[rmunn]

I don't think this is quite the right solution. I think in addition to checking if the token to be exploded is a Value, we also need to check if the previous token is a Name. I'll try to create a unit test that proves that.

BTW, I'm currently working on a fix for #396 that looks like it's going to end up fixing #420 at the same time, so once that PR is submitted I'll link to it from this one as well.

[rmunn]

Here's a unit test that fails with this PR, but works if you also check that the previous token is a Name:

[Fact]
public static void Values_with_same_name_as_sequence_option_do_not_cause_later_values_to_split_on_separators()
{
    var args = new[] { "c", "x,y" };
    var tokensExpected = new[] { Token.Value("c"), Token.Value("x,y") };
    var typeInfo = typeof(OptionsWithSeparator);

    var specProps = typeInfo.GetSpecifications(pi => SpecificationProperty.Create(
            Specification.FromProperty(pi), pi, Maybe.Nothing<object>()))
        .Select(sp => sp.Specification)
        .OfType<OptionSpecification>();

    var tokenizerResult = Tokenizer.ConfigureTokenizer(StringComparer.InvariantCulture, false, false)(args, specProps);
    var tokens = tokenizerResult.SucceededWith();
    tokens.Should().BeEquivalentTo(tokensExpected);
}

internal class OptionsWithSeparator
{
        [Option('f', "flag", HelpText = "Flag")]
        public bool Flag { get; set; }

        [Option('c', "categories", Required = false, Separator = ',', HelpText = "Categories")]
        public IEnumerable<string> Categories { get; set; }

        [Option('j', "jobId", Required = true, HelpText = "Texts.ExplainJob")]
        public int JobId { get; set; }
}

[rmunn]

47618e0 (part of #684) is a better fix, which fixes the unit test in #672 (comment) that fails with this PR.