Move various parsers/formatters into HttpAbstractions

[davidfowl]

In our continued effort to provide generally useful abstractions for the greater ecosystem, we should move the low level parsers and formatters into Microsoft.AspNetCore.WebUtilities.

HTTP Parser from Kestrel - https://github.com/aspnet/KestrelHttpServer/blob/59b77bb357f50946ecea310feb8db53473e0e165/src/Kestrel.Core/Internal/Http/HttpParser.cs

The chunked encoding parser from Kestrel - https://github.com/aspnet/KestrelHttpServer/blob/59b77bb357f50946ecea310feb8db53473e0e165/src/Kestrel.Core/Internal/Http/MessageBody.cs#L475

HPackEncoder and HpackDecoder - https://github.com/aspnet/KestrelHttpServer/blob/59b77bb357f50946ecea310feb8db53473e0e165/src/Kestrel.Core/Internal/Http2/HPack/HPackDecoder.cs
https://github.com/aspnet/KestrelHttpServer/blob/59b77bb357f50946ecea310feb8db53473e0e165/src/Kestrel.Core/Internal/Http2/HPack/HPackEncoder.cs

[muratg]

@davidfowl putting this into the next milestone.

Was Managed HttpClient a potential user of this in your mind? Any other users?

[daniel-white]

The multipart support would be nice to consider too!

[litichevskiydv]

Will it be possible to use output and input formatters such as JSON output formatters in the middlewares?

[khellang]

It might be soon; aspnet/Mvc#6822 (comment), aspnet/Diagnostics#346 and aspnet/Mvc#6998

[aspnet-hello]

This issue was moved to dotnet/aspnetcore#2324