Dakota Johnson and Chris Martin are still going strong. After shutting down split rumors, insiders close to the Hollywood power couple claim they’re doing better than ever in their longtime romance. “Their relationship works because they are both very independent and actually have lives outside of their relationship too,” a source said of Johnson, 34, and Martin, 47. “It’s like every time they are not spotted together for a while, there are breakup rumors.” The Madame Web actress and the Coldplay frontman have been together since 2017 and quietly got engaged at some point in their nearly seven…