Change IConsole to ConsoleStreams or equivalent

[jonsequitur]

Because IConsole was in part intended to explore future potential ideas for System.Console which will require a longer design period, we should change this interface to a concrete type with a more focused scope.

A suggestion made by @terrajobst in API review looked roughly like this:

public class ConsoleStreams
{
    public TextWriter StandardOutput { get; }
    public TextWriter StandardError { get; }
    public TextReader StandardInput { get; }
}

[KalleOlaviNiemitalo]

For piping binary data as described in #1782 (comment), I'd also like

public Stream OpenStandardInput();
public Stream OpenStandardOutput();
public bool IsInputRedirected { get; }
public bool IsOutputRedirected { get; }

I don't use binary I/O on StandardError, though.

[jonsequitur]

These changes would be out of scope for the purpose of this issue (although simpler handling of piped input is something we'd like to look at after the 2.0 GA). It's possible we'll leave input out as well since by default, attempting to read from it will likely result in a blocking and non-cancellable call.

I'd encourage you to add your thoughts to this discussion: dotnet/runtime#52374. Until some of these design concerns are resolved, it's unlikely we'll try to address them in System.CommandLine.

[adamsitnik]

fixed by #2106