A Southtown restaurant under construction for nearly three years at the historic site of another longtime café is set to open Friday. The Tex-Mex eatery Rosario’s — now called Rosario’s ComidaMex & Bar — reopens February 10 at the site of longtime diner El Mirador as a contemporary, two-story venue with a rooftop bar. Rosario’s formerly occupied an older stucco building on South Alamo Street….