Darling Grenadine, which opens off-Broadway on February 10, marks Roundabout Theatre Company's first debut of a new musical in 10 years. A Manhattan love story between a charming songwriter and tenacious chorus girl, Darling Grenadine stars The Band Visit's Adam Kantor and Come From Away's Emily Walton. The new musical features a book and score from Daniel Zaitchik, and direction and cho…