Provide a better error message when TransportMaxBufferSize exceeded in a single message

[analogrelay]

Right now, if you send a single message that serializes to larger than 32KB, you get:

fail: Microsoft.AspNetCore.SignalR.HubConnectionHandler[2]
      Error when processing requests.
System.InvalidOperationException: Advancing examined to the end would cause pipe to deadlock because FlushAsync is waiting.
   at System.IO.Pipelines.ThrowHelper.ThrowInvalidOperationException_BackpressureDeadlock()
   at System.IO.Pipelines.Pipe.AdvanceReader(BufferSegment consumedSegment, Int32 consumedIndex, BufferSegment examinedSegment, Int32 examinedIndex)
   at System.IO.Pipelines.Pipe.AdvanceReader(SequencePosition& consumed, SequencePosition& examined)
   at System.IO.Pipelines.Pipe.DefaultPipeReader.AdvanceTo(SequencePosition consumed, SequencePosition examined)
   at Microsoft.AspNetCore.SignalR.HubConnectionHandler`1.DispatchMessagesAsync(HubConnectionContext connection)
   at Microsoft.AspNetCore.SignalR.HubConnectionHandler`1.RunHubAsync(HubConnectionContext connection)
   
   fail: Microsoft.AspNetCore.SignalR.HubConnectionHandler[2]
      Error when processing requests.
System.InvalidOperationException: Advancing examined to the end would cause pipe to deadlock because FlushAsync is waiting.
   at System.IO.Pipelines.ThrowHelper.ThrowInvalidOperationException_BackpressureDeadlock()
   at System.IO.Pipelines.Pipe.AdvanceReader(BufferSegment consumedSegment, Int32 consumedIndex, BufferSegment examinedSegment, Int32 examinedIndex)
   at System.IO.Pipelines.Pipe.AdvanceReader(SequencePosition& consumed, SequencePosition& examined)
   at System.IO.Pipelines.Pipe.DefaultPipeReader.AdvanceTo(SequencePosition consumed, SequencePosition examined)
   at Microsoft.AspNetCore.SignalR.HubConnectionHandler`1.DispatchMessagesAsync(HubConnectionContext connection)
   at Microsoft.AspNetCore.SignalR.HubConnectionHandler`1.RunHubAsync(HubConnectionContext connection)

These errors are unpleasant. They occur because we are trying to read a single message that is larger than the backpressure size. We should provide a better error message in this case (heck, even if it takes just catching the exception). Something like "Message exceeded the maximum buffer size of {TransportMaxBufferSize} bytes"

It may be difficult to do this though, so we'll need to design this a bit (and may decide it's not feasible in the process).

[analogrelay]

If we flow the maximum buffer size down to the reader, we can do this by checking the buffer size when TryParseMessage returns false and if it's equal to or greater than the maximum buffer size, we know this exception will occur and can throw our own better exception ("Message exceeded maxmium size").

[analogrelay]

https://github.com/dotnet/corefx/issues/30894 should resolve this sufficiently.

[muratg]

(This is just tracking dotnet/corefx#30894)