“Little Simz is unflinching. The London rapper’s fans show up for her elastic, relentless rhymes, but they stay for her candor. On “Backseat,” her first release since last year's Stillness In Wonderland, she continues her no-nonsense approach, but this time turns inward. Her adversary is the disillusion and isolation that the spotlight often brings—success can be knotty that way. By her own admissi”