Move Int64 parsing logic to HttpAbstractions

[JunTaoLuo]

The logic in

KestrelHttpServer/src/Microsoft.AspNetCore.Server.Kestrel/Internal/Http/FrameHeaders.cs

Line 235 in 2940895

public static unsafe long ParseContentLength(StringValues value)

should be moved to Abstractions to allow other repos to take advantage of the performance boost.

[Tratcher]

Especially request and response content-length headers

[JunTaoLuo]

Done in https://github.com/aspnet/KestrelHttpServer/pull/1228/files