NamedPipeClientStream Connect can use uninitialized _normalizedPipePath

When adding nullable annotations for System.Net.Sockets (#32675), it was discovered that there is a scenario when using NamedPipeClientStream can use a null string:

When calling NamedPipeClientStream.Connect on Unix, it will try using the _normalizedPipePath string:

https://github.com/dotnet/runtime/blob/032e8dbd0ca5aee045a41ff78e3c0244d3ec3b51/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.Unix.cs#L21-L31

However, if the NamedPipeClientStream object was created with the constructor that takes an existing SafePipeHandle and isConnected: false, then _normalizedPipePath will be null.

https://github.com/dotnet/runtime/blob/032e8dbd0ca5aee045a41ff78e3c0244d3ec3b51/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.cs#L101-L103

Doing some searching, I'm honestly not certain how this scenario (existing SafePipeHandle and isConnected: false) can ever work successfully. It will need a path to be able to connect to, which it wasn't given. So at best we may be able to throw a better exception than the ArgumentNullException we get:

Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'path')
   at System.Net.Sockets.UnixDomainSocketEndPoint..ctor(String path)
   at System.IO.Pipes.NamedPipeClientStream.TryConnect(Int32 timeout, CancellationToken cancellationToken)
   at System.IO.Pipes.NamedPipeClientStream.ConnectInternal(Int32 timeout, CancellationToken cancellationToken, Int32 startTime)
   at System.IO.Pipes.NamedPipeClientStream.Connect(Int32 timeout)
   at System.IO.Pipes.NamedPipeClientStream.Connect()

/cc @stephentoub