Add attempt count to Policy.ExecuteAndCaptureAsync(...), ref Polly #73

extracted_from_PolicyAsync.cs

 public async Task<PolicyResult<TResult>> ExecuteAndCaptureAsync<TResult>(Func<CancellationToken, Task<TResult>> action, CancellationToken cancellationToken, bool continueOnCapturedContext)
        {
            if (_asyncExceptionPolicy == null) throw new InvalidOperationException(
                "Please use the asynchronous RetryAsync, RetryForeverAsync, WaitAndRetryAsync or CircuitBreakerAsync methods when calling the asynchronous Execute method.");

            try
            {
                var result = default(TResult);
                int attempts = 0; // Added
                await _asyncExceptionPolicy(async ct =>
                {
                    attempts++; // Added
                    result = await action(ct).ConfigureAwait(continueOnCapturedContext);
                }, cancellationToken, continueOnCapturedContext)
                .ConfigureAwait(continueOnCapturedContext);

                return PolicyResult<TResult>.Successful(result); // Extend to be .Successful(result, attempts)
            }
            catch (Exception exception)
            {
                return PolicyResult<TResult>.Failure(exception, GetExceptionType(_exceptionPredicates, exception)); // Extend to add attempts to .Failure(...) signature
            }
        }