Move Invoke* and Parse extension methods to their extended Symbol types #1905
Description
// All of these should be instance methods.
public static class CommandExtensions
{
public static int Invoke(this Command command, string[] args, IConsole console = null);
public static int Invoke(this Command command, string commandLine, IConsole console = null);
public static Task<int> InvokeAsync(this Command command, string[] args, IConsole console = null);
public static Task<int> InvokeAsync(this Command command, string commandLine, IConsole console = null);
// The comments from Argument(Extensions)::Parse also apply here.
public static ParseResult Parse(this Command command, string[] args);
public static ParseResult Parse(this Command command, string commandLine);
}