WasmFS: NodeFS ino numbers in directory listings

`wasmfs.test_readdir_rawfs` fails because we return a zero ino. That is the zero at the end here:

https://github.com/emscripten-core/emscripten/blob/b76fdf445f0a8dfdebfd0f67749bfbc20665d397/system/lib/wasmfs/backends/node_backend.cpp#L274

Overall IIUC, in NodeFS when we do readdir then we tell node to scan the directory for items, but we do *not* build WasmFS nodes for them. Such a node is necessary to get an ino.

I'm not sure how important this is - it might be fine to just keep returning 0 for the ino, for now.