Add Pipelines support for DuplexStream

[scalablecory]

PipeWriter's PipeWriterStream could reasonably support completing writes, so we should consider making it implement DuplexStream. It is not technically a duplex stream and could make things messy if we add more APIs onto DuplexStream. That said, anyone using the wrapper is already only using it only for writes, so it wouldn't be horrible to just have it throw on any future read-specific DuplexStream APIs.

Alternately to avoid any confusion, we could add a new DuplexStream-based type for wrapping a PipeWriter/PipeReader.

[stephentoub]

Alternately to avoid any confusion, we could add a new DuplexStream-based type for wrapping a PipeWriter/PipeReader.

How about an extension on IDuplexPipe that creates a DuplexStream? Might also want the inverse.

[davidfowl]

There are a bunch of types I want to add to the pipelines assembly that are always needed for doing duplex things. We should do them en-masse:

• https://github.com/dotnet/aspnetcore/blob/main/src/Shared/ServerInfrastructure/DuplexPipeStream.cs
• https://github.com/dotnet/aspnetcore/blob/main/src/Shared/ServerInfrastructure/DuplexPipe.cs
• https://github.com/dotnet/aspnetcore/blob/main/src/Shared/ServerInfrastructure/DuplexPipeStreamAdapter.cs