Update dependencies from https://github.com/aspnet/AspNetCore-Tooling build 20191205.6 (#17624)

- Microsoft.AspNetCore.Mvc.Razor.Extensions - 3.1.1-servicing.19605.6
- Microsoft.AspNetCore.Razor.Language - 3.1.1-servicing.19605.6
- Microsoft.CodeAnalysis.Razor - 3.1.1-servicing.19605.6
- Microsoft.NET.Sdk.Razor - 3.1.1-servicing.19605.6