Paul Mescal and Patsy Ferran battle it out in the Almeida's new production of a poetic drama whose ambiguity is enthralling Tennessee Williams's old bus keeps on running. The Almeida's production of A Streetcar Named Desire, starring Patsy Ferran and directed by Rebecca Frecknall, is the play's fifth major UK revival in the last 20 years. That's not bad going for a work that at its 1947 New York premiere was describe…