Support target-type new expressions.

Right now this fails to parse:

        internal static class EnumFormatters
        {
            public static readonly EnumFormatter<AnalysisKind> AnalysisKind = new(value => (int)value, value => (AnalysisKind)value);
        }

failing at the = new( bit. I think this is the relevant piece of syntax.

[initram]

The new without a type is a new C# 9 feature called target-type new expressions. This is the issue for it: https://github.com/dotnet/csharplang/issues/100

So it is simply a new feature, not really a bug in the current syntax.

[initram]

I think this issue can be closed now.