Long considered a tech hinterland, Southeast Asia is fast emerging as a center of gravity for the industry.The CEOs of Apple Inc., Microsoft Corp. and Nvidia Corp. are among the industry chieftains who’ve swung through the region in past months, committing billions of dollars in investment and holding forth with heads of state from Indonesia to Malaysia. Amazon.com Inc. just this week took over a giant conference hall in downtown Singapore to unfurl a $9 billion investment plan before a thousand...