Andrew Garfield may have just added fuel to one of Marvel fans' biggest Avengers: Doomsday theories after appearing to suggest that the mysterious Spider-Man detected in the post-credits scene of Spider-Man: Brand New Day could be Miles Morales. The actor was asked about the film's mysterious final tease, in which the Spidey Tracker appears to detect a Spider-Man somewhere off Earth. When the interviewer suggested the signal could belong to Tobe…