Remove Content-Encoding and Content-Length from responses in NSUrlSessionHandler for automatically decompressed content

[rolfbjarne]

All other http handlers (SocketsHttpHandler, WinHttpHandler, Android's http handler) remove the Content-Encoding + Content-Length headers if the returned content was automatically decompressed.

References:

• ProtocolException with iOS .NET 6.0 Application: The number of bytes available is inconsistent with the HTTP Content-Length header. wcf#4903 (comment)
• [Android] Deserialization issue when consuming ASMX Web Service runtime#80935
• Tweak AndroidMessageHandler behavior for WCF support android#7785
• Accessing original Content-Encoding header in HttpResponseMessage runtime#42789 (comment)
• https://github.com/dotnet/runtime/blob/b2974279efd059efaa17f359ed4b266b1c705721/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/DecompressionHandler.cs#L122-L123
• Remove content headers in CurlHandler when automatically decompressed corefx#6799

We should be compatible with the other http handlers and do the same thing.

This should fix dotnet/wcf#4903.