TAIPEI, Taiwan—Much of Asia has largely managed to keep Omicron at bay even as the variant rages in other parts of the world, but the region that is home to most of the globe’s population is bracing for what may be an inevitable surge. Strict quarantine rules for arrivals and widespread mask wearing have helped slow the spread of the highly contagious variant in Asia. Countries such as Japan, South Korea and Thailand quickly reinstated entry and quarantine restrictions in recent weeks after relaxing them in the fall. But cases are mounting, and experts say the next few months will be critical….