Move various parsers/formatters into HttpAbstractions

[aspnet-hello]

From @davidfowl on Saturday, August 19, 2017 2:37:24 PM

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

Copied from original issue: aspnet/HttpAbstractions#916

[aspnet-hello]

From @muratg on Monday, October 30, 2017 10:41:22 AM

@davidfowl putting this into the next milestone.

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

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From @daniel-white on Monday, November 13, 2017 8:28:46 AM

The multipart support would be nice to consider too!

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From @litichevskiydv on Monday, December 11, 2017 10:13:37 AM

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

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From @khellang on Monday, December 11, 2017 10:30:50 AM

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