Provide better experience when the BodyReader is left in a reading state

When middleware calls HttpContext.Request.BodyReader.ReadAsync() and exits without calling HttpContext.Request.BodyReader.AdvanceTo(), Kestrel will fail to read the following request while logging the following exception as a warning (at least for Content-Length HTTP/1.1 requests, not sure about others):

System.InvalidOperationException
  HResult=0x80131509
  Message=Reading is already in progress.
  Source=Microsoft.AspNetCore.Server.Kestrel.Core
  StackTrace:
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.Http1ContentLengthMessageBody.TryReadInternal(ReadResult& readResult) in /_/src/Servers/Kestrel/Core/src/Internal/Http/Http1ContentLengthMessageBody.cs:line 126

This is pretty common type of error when something throws in between calls to ReadAsync() and AdvanceTo() and AdvanceTo() isn't in a finally block.

It would be better if Kestrel logged a warning that explicitly tells the developer that there's a missing call to BodyReader.AdvanceTo(). Better yet would be to recover from this situation by draining the rest of the request despite the BodyReader being left in a bad state so that the connection can still be used for future requests.

We should also ensure Kestrel handles the BodyWriter being left in a bad state gracefully.

See #17723 and #14727 (In that case it was Kestrel itself throwing without properly advancing the connection pipe though).

• ASP.NET Core version 3.1