Volvo, the auto maker that spent 90 years polishing a reputation for safety, indicated Wednesday it is mounting an ambitious challenge to Tesla Inc.’s electric cars. But the even tougher news for Tesla’s billionaire founder, Elon Musk, is that the Scandinavian company isn’t the only deep-pocketed rival planning to compete with the Silicon Valley pioneer. Nearly all global vehicle makers are mounting their own electric-car push,…