Redirect should encode URLs if it needs to

All these issues are result of people trying to redirect to a URL that is not all ASCII. Resolution seems to be "you should have encoded your URL".

https://github.com/aspnet/Home/issues/2678
https://github.com/aspnet/Mvc/issues/7701
https://github.com/aspnet/KestrelHttpServer/issues/2508
https://github.com/aspnet/KestrelHttpServer/issues/2296
https://github.com/aspnet/Security/issues/1646
https://github.com/aspnet/HttpAbstractions/issues/971
https://github.com/aspnet/Routing/issues/513
https://github.com/aspnet/Mvc/issues/7529
https://github.com/aspnet/HttpAbstractions/issues/907
https://github.com/aspnet/Mvc/issues/6609
https://github.com/aspnet/Home/issues/2106
https://github.com/madskristensen/Miniblog.Core/issues/87
https://github.com/dotnet/aspnetcore/issues/37337 (unicode host)

However, the fact that the RedirectResult puts the URL into a HTTP header (which is the ultimate source of the issue) is an implementation detail that the caller cannot magically assume. It is therefore responsibility of e.g. RedirectResultExecutor to meet the requirements and ensure the URL is properly formatted in case it decides to use HTTP headers for redirection.