E.T. the Extra-Terrestrial was one of the highest-grossing films ever made, but director Steven Spielberg always resisted making a followup to his 1982 film about an alien left behind on earth who befriends a young boy and attempts to “phone home.” However, E.T. and Elliott have finally reunited 37 years later—not for a sequel, but for an Xfinity spot about how technology brings people together. In the ad, which debuted Thursday morning during the Macy’s Thanksgiving Day Parade on NBC,…