“Radiant Baby” the new musical about the life of artist Keith Haring, opens on Broadway. Nice try, but “the show never brings either Haring or his world into crisp focus, relying instead on a blurry shorthand of artist-bio clichés (the agony, the ecstasy, the egomania, the triumph of the creative spirit) and composite social archetypes. Haring’s insistently vital art is so spectacularly in evidence — thanks to the splendid projection designs of Batwin and Robin Productions — which only underscores the musical’s limitations.”