Update to support CancellationToken

[NoahSurprenant]

Hello, I was running into issues while attempting to generate my TypeScript when my receiver interface had a CancellatonToken parameter. Upon investigation, I only found this issue #87 but no solution was mentioned. In my use case the CancellationToken is found on the Receiver and not the Hub, and I am not streaming. I am opening this PR to allow the generation with CancellationToken, and updating the analyzer to ignore CancellationTokens found on the Receiver

[nenoNaninu]

Thanks for the PR. However, SignalR does not propagate CancellationToken from server to client. In what use case do we need the CancellationToke as a parameter to the receiver's method? It would be helpful if you show me examples.

[nenoNaninu]

Investigation showed that SignalR handles cases where the last parameter of a strongly typed caller's method is a CancellationToken specially.

public interface IHub
{
    Task M0();
}

public interface IReceiver
{
    Task M1(CancellationToken cancellationToken); // OK
    Task M2(int value, CancellationToken cancellationToken); // OK
    Task M3(CancellationToken cancellationToken, int value); // Serialization Error
}

public class MyHub : Hub<IReceiver>, IHub
{
    private readonly ILogger<MyHub> _logger;

    public MyHub(ILogger<MyHub> logger)
    {
        _logger = logger;
    }

    public async Task M0()
    {
        var cts = new CancellationTokenSource();

        try
        {
            await this.Clients.Caller.M1(cts.Token); // OK
            await this.Clients.Caller.M2(99, cts.Token); // OK
            await this.Clients.Caller.M3(cts.Token, 99); // Serialization Error
        }
        catch (Exception exception)
        {
            _logger.LogError(exception, "MyHub.M0");
        }
        finally
        {
            cts.Cancel();
            cts.Dispose();
        }
    }
}

HubConnection connection = ...;

var hub = connection.CreateHubProxy<IHub>();

connection.On("M1", () =>
{
    Console.WriteLine("M1");
});

connection.On<int>("M2", value =>
{
    Console.WriteLine($"M2: {value}");
});

await connection.StartAsync();

await hub.M0();

[nenoNaninu]

Thanks for the PR!