Better API for hairy cases.

[JohanLarsson]

    public partial class ValidCode
    {
        public static class StyletMvvm
        {
            private static readonly AssertSettings AssertSettings = AssertSettings.Create(
                new Analyzer(),
                ExpectedDiagnostic.Create(),
                MetadataReferences.Transistive(typeof()));

            [Test]
            public static void SomeTest()
            {
                var code = @"
namespace N
{
    public class C
    {
    }
}";

                RoslynAssert.Valid(code, AssertSettings);
            }

Less noise in config scenarios.
We can remove a bunch of overloads.