Turbopack: sourcemaps for JSON modules (#84611)
Closes PACK-5637
Generate sourcemaps for JSON modules, which better attributes bundle sizes in tools such as source-map-explorer
(These should never show up in stack traces)
<img width="1509" height="502" alt="Bildschirmfoto 2025-10-07 um 17 03 00" src="https://github.com/user-attachments/assets/0c41bade-36cd-417a-b32d-f5cc3dfe3a7a" />
<img width="374" height="470" alt="Bildschirmfoto 2025-10-07 um 15 01 14" src="https://github.com/user-attachments/assets/a93d322e-cca2-4624-ba6c-d23febc3fa87" />
