Riverside Studios, LondonJenna Russell gives a shining performance of quiet resolve in this musical adaptation of Paul Gallico's novel about a widowed cleaner in gloomy postwar London who sets her sights on purchasing a Dior dress in Paris The set for this new production of a poignant 2016 musical is all doors. Nik Corrall's design suggests that its heroine, Ada Harris (Jenna Russell), might be opening up new opportu…