A documentary born out of isolation, “Charli XCX: Alone Together” feels stuck in one place. It’s built on a high concept gambit: the world shuts down and pop dynamo Chari XCX is stuck in her L.A. home with nowhere to go and nothing to do. Feeling creatively restless, she decides to write, record and release a new album in a five week period, documenting the process in real time for her fans online. Sounds thrilling, right? Guess you had to be there. “Alone Together” treats the creation of XCX’s 2020 album “How I’m Feeling Now” as background fodder and instead focuses on the artist’s connection…