Tesla Inc. is headed for its highest-profile trial yet over a crash blamed on Autopilot, the driver-assistance system Elon Musk has billed as crucial to his pursuit of self-driving cars.The electric-vehicle maker prevailed in two previous trials in California after juries found the accidents, one fatal and one not, were due to driver error rather than the company’s technology. Each of the trials — and more that are scheduled in coming months in California and Florida — clash with Musk’s mantra t...