Cirque du Soleil’s latest extravaganza, Luzia, draws on a Mexican theme for its storyline, but in a way that proves more accessible than some of the earlier productions. It’s subtitled “A Waking Dream of Mexico,” and under that guise it presents the feats of strength, agility and clowning with less obligation to a plot that can feel murky. An announcer sets it all up: he is a pilot of Flight 2016 to Mexico; the audience is in the passenger seats; and as the plane takes off, the fliers are meant to relax and doze into an in-flight fantasia.