HAL.Bitmap: speedup Set/Get_Pixel and use common code for offset calculation.
HAL.Bitmap: speedup Set/Get_Pixel and use common code for offset calculation.

simonjwright/Ada_Drivers_Library,ellamosi/Ada_BMP_Library,lambourg/Ada_Drivers_Library,AdaCore/Ada_Drivers_Library,simonjwright/Ada_Drivers_Library,AdaCore/Ada_Drivers_Library,Fabien-Chouteau/Ada_Drivers_Library,Fabien-Chouteau/Ada_Drivers_Library