Combine WasmFS fetch backend with OPFS backend

[mmarczell-graphisoft]

My usecase is: fetch a really large file (up to a few GBs) once and then store it locally. The current fetch backend for WasmFS stores the downloaded files in memory. It would be great if it could instead store them in OPFS which the browser maps to actual files on the physical drive.

[thearperson]

+1