WasmFS: NODERAWFS

As of #19400 basic NODERAWFS support is present, but we are missing two things at least:

1. Current support mounts the current directory as the NodeFS root. That works for just writing files to the current real directory, but you can't look up out of it (e.g. you can't read `/tmp/something` if you began in `/usr/home/me`). Mounting `/` instead of `.` as that PR does might help but it didn't just work when I tried it, but it might be a start.
2. NODERAWFS doesn't just mount NODEFS but it also apparently forwards in a more direct manner to the underlying Node APIs. I'm not sure of the details there. @sbc100 suggested perhaps implementing NODERAWFS using a replacement syscall layer, which would work for both WasmFS and otherwise. I am not sure of how important that is, though - I'm still going through tests and have not seen a failure yet, but more remain to be tested.