Retailers in Vietnam just spilled the beans on Samsung’s upcoming tablet lineup well ahead of schedule. A fresh leak gives us a complete preview of the official Book Cover Keyboard Slim and Pro Keyboard for the Samsung Galaxy Tab S12+, showing off clear press renders and retail box packaging before the company could even announce them. These leaked images not only give us a close look at the keyboard accessories from multiple angles. They also confirm the overall design of the slate itself, including a sleek new default wallpaper. Design-wise, Samsung isn’t reinventing the wheel here. The Korean tech giant…