[Design] Add `<select/>` tag helper

- #1248

"[Design]" just for missing unit tests. Otherwise complete.
/cc @NTaylorMullen 
nit: Tempted to use `<c>` for the values.  SOmewhat like we do here:
https://github.com/aspnet/Mvc/blob/dev/src/Microsoft.AspNet.Mvc.TagHelpers/ValidationSummaryTagHelper.cs#L29-L30