Call it Charli ’s law: When she finds herself at a precarious position on the food chain, the savvy pop singer builds her own biosphere. What even constitutes “radio pop” these days is so atomized, and those precious few top spots are by and large reserved for either country artists or Taylor Swift and her disciples . So what was Zara Larsson to do when a dolphin meme and an opening slot for Tate McRae made her gay-Twitter-famous and then famous-famous? Plan a Girls Trip . Brat and it’s completely different but also still brat (and really Pop 2 before it) laid the blueprint, and Fancy Some More? codified the form. But Larsson’s may be the first remix album in recent memory to arrive with greater anticipation than its progenitor. Larsson had her biggest break yet with her guest turn on PinkPantheress ’ “Stateside” rework, and she’s repaid the favor in kind. “Midnight Sun (Girls Trip)” has it almost too easy.…