Shares of the German sportscar maker Porsche slid on Tuesday after the company slashed its full-year revenue forecast. The automaker warned that a snarled supply chain involving aluminum parts from a supplier could limit or even halt production of specific models. Porsche now forecasts a return on sales between 14% and 15% for the year, down from its previous estimate of around 15% to 17%. The company faces a slowdown in sales in the Chinese market, driving global deliveries down 7% in the first half of the year. The company…