Gary Sanchez’s titanic blast helps Yankees bail out Aroldis Chapman

ST. PETERSBURG, Fla. — As the ball climbed toward Tropicana Field’s gray roof, you could almost hear Brian Cashman’s offseason mantra every time a trade rumor involving Gary Sanchez surfaced. “He is our starting catcher,’’ the GM repeated often despite Sanchez’s brutal 2018 season behind the plate catching and alongside it with a bat in…