A popular fast-casual burger chain has introduced new restaurant prototypes as part of its growth plans.San Antonio-based Whataburger plans to roll out two new restaurant designs by early 2027, with construction expected to start later this year.The new designs — dubbed The Legacy and The Essential — draw on Whataburger’s 75-year history, reviving past architectural elements.The prototypes will debut first in Texas and will be followed by openin…