In India, dosas are cooked on a griddle in the street, as well as in restaurants and homes. As street food goes, the dosa gets high marks. It’s not junk, and it tastes great. The Dosa Factory in Central Square, subtitled “Indian Street Food,” is a hole-in-the-wall–not for an evening of food and talk. But that’s not what street food is. It’s a quick fix, and for these purposes, it’s about as good as it gets.