It’s been more than 18 months since Apple Inc. last updated its iPad line, marking the longest gap in new models since Steve Jobs first unveiled the product in 2010. The drought finally ends on May 7.That’s the day Chief Executive Officer Tim Cook is poised to introduce major upgrades to the iPad Pro and iPad Air, as well as new versions of the tablet’s accessories. The company is delivering the news through an online event dubbed “Let Loose” that’s expected to last a little more than half an ho...