Implementing default getOSFileInfo implementation

[tryggvil]

Implementation of getOSFileInfo for other platforms such as wasm

[willscott]

Is your use case just for wasm?

the stub for windows is probably the 'safe' default case - because there isn't a guarantee in the default case that the fields you use off of syscall.Stat_t will exist. If you want to have this build as a wasm-specific implementation, that would be okay.

[tryggvil]

Yes my case right now is specifically wasm.
So I updated to have a specific implementation that works on wasm and fall back to the same implementation as windows.

[tryggvil]

Also updated go-billy to v5.6.0