Prefer the new encoders over the old WebUtility APIs

[GrabYourPitchforks]

There are still some call sites in the StaticFiles code base that invoke WebUtility.HtmlEncode. These call sites should instead use IHtmlEncoder.HtmlEncoder.

[Praburaj]

How should I get this service from static files. Can I instantiate an object of type HtmlEncode?

[GrabYourPitchforks]

The types IHtmlEncoder, IJavaScriptStringEncoder, and IUrlEncoder are in the Microsoft.AspNet.WebUtilities package. To register them from within your own AddServices method, reference the Microsoft.AspNet.Http.Extensions package and call the AddEncoders extension method on IServiceCollection.