“Supergirl” is a very good, polished pilot, which, in TV terms, might be one of the least interesting questions hovering around this latest DC Comics adaptation from producers Greg Berlanti and Andrew Kreisberg. The introductory hour hews closely to that pair’s formula for “The Flash,” from elevating an adorable “Glee” alum (there Grant Gustin, here Melissa Benoist) to costumed-icon status, to the it-takes-a-village approach to raising a superhero, with plenty of people in on the character’s secret virtually from the get-go. All that, however, belies the main issue: Can such fare fly on CBS? On the plus side, finding the right star, and constructing a credible pilot, are big parts of the battle. Thanks to those strengths, if the producers can sustain the playfulness and action without going overboard on Flockhart’s character, there’s reason to believe this “girl” can fly.