“Rebbeca,” a new documentary centered on Mexican-American singer and actress Becky G , isn’t simply a highlight reel of her achievements. Yes, it offers an up-close view of the star’s ascent — from her exhilarating first headlining tour to the bold creation of her música mexicana album “ Esquinas .” Yet what emerges is a deeper story of a young woman confronting the past and reclaiming her power through personal reckoning, family lineage and forgiveness. “Rebbeca was saved by Becky G,” she