[3.1] Add latin1 support to IIS (#22798)

...rs/HttpSys/src/Microsoft.AspNetCore.Server.HttpSys.csproj

src/Servers/IIS/IIS/src/Core/IISHttpContext.cs

src/Servers/IIS/IIS/src/Core/IISHttpContextOfT.cs

src/Servers/IIS/IIS/src/Core/IISHttpServer.cs

...ervers/IIS/IIS/src/Microsoft.AspNetCore.Server.IIS.csproj

.../IIS/test/Common.FunctionalTests/Inprocess/Latin1Tests.cs

...S/IIS/test/IIS.FunctionalTests/IIS.FunctionalTests.csproj

...ler.FunctionalTests/IIS.NewHandler.FunctionalTests.csproj

...ewShim.FunctionalTests/IIS.NewShim.FunctionalTests.csproj

...Express.FunctionalTests/IISExpress.FunctionalTests.csproj

...rvers/IIS/IIS/test/testassets/InProcessWebSite/Program.cs

...rvers/IIS/IIS/test/testassets/InProcessWebSite/Startup.cs

...Kestrel/Core/src/Internal/Infrastructure/HttpUtilities.cs

.../Core/src/Microsoft.AspNetCore.Server.Kestrel.Core.csproj

src/Shared/HttpSys/RequestProcessing/HeaderEncoding.cs

src/Shared/HttpSys/RequestProcessing/NativeRequestContext.cs

src/Shared/ServerInfrastructure/StringUtilities.cs

...est/Shared.Tests/Microsoft.AspNetCore.Shared.Tests.csproj