A decade ago, Ellie Goulding was suddenly thrust into the spotlight with her massive worldwide hit “Lights,” and it was a tricky transition for the shy singer-songwriter, who has since confessed that she was unprepared for fame. The endless cycle of touring and promotion that followed, through 2015’s platinum-selling Delirium, took its toll. But after taking a nearly five-year break between full-length studio albums to enjoy a relatively anonymous existence in the States, the British pop star is back with her fourth LP, the ambitious, 18-song Brightest Blue — and she’s in a good place mentally as well as artistically.