"Connection: close" is not respected when httpsys server response HEAD request with body

[erhuan-msft]

Describe the bug

On Asp.Net Core 2.2, httpsys server does not automatically remove response body on HEAD request. This means the server will respond with mal-formed response. In the particular case where the HEAD request comes with "Connection: Close" header, server will response with "Connection: Close" header but does not close the connection on the server end. This causes the server to have too many open connections.

To Reproduce

Steps to reproduce the behavior:

1. Use Asp.Net Core 2.2
2. Create hello world Asp.Net Core project using "dotnet new web"
3. Use HttpSys instead of Kestrel, as demonstrated in edit in Program.cs below

        public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .UseHttpSys()
                .UseStartup<Startup>();

4. Build with "dotnet build"
5. Start the server with "dotnet run --no-launch-profile"
6. In another console, curl a HEAD request

curl.exe http://localhost:5000 --HEAD -H "Connection: Close" -v

7. Server responses with a body & Server TCP connection will be kept in CLOSE_WAIT indicating the server did not close the TCP connection.

* Rebuilt URL to: http://localhost:5000/
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 5000 (#0)
> HEAD / HTTP/1.1
> Host: localhost:5000
> User-Agent: curl/7.55.1
> Accept: */*
> Connection: Close
>
< HTTP/1.1 200 OK
HTTP/1.1 200 OK
< Transfer-Encoding: chunked
Transfer-Encoding: chunked
< Server: Microsoft-HTTPAPI/2.0
Server: Microsoft-HTTPAPI/2.0
< Date: Sun, 13 Jan 2019 17:19:45 GMT
Date: Sun, 13 Jan 2019 17:19:45 GMT
< Connection: close
Connection: close

<
* Excess found in a non pipelined read: excess = 17 url = / (zero-length body)
* Closing connection 0
C:\work> netstat -an | findstr 5000
  TCP    0.0.0.0:5000           0.0.0.0:0              LISTENING
  TCP    [::]:5000              [::]:0                 LISTENING
  TCP    [::1]:5000             [::1]:5640             CLOSE_WAIT
  TCP    [::1]:5640             [::1]:5000             FIN_WAIT_2

Expected behavior

Either HttpSys should handle HEAD request automatically like Kestrel or it should respect "Connection: Close" header by closing the connection. It is very easy to NOT handle HEAD request.

Additional context

This issue is related to the following issue: #5881