Function fd_readdir

pub fn fd_readdir<M: Memory>(
    ctx: &mut WasiCtx,
    mem: &mut M,
    fd: __wasi_fd_t,
    buf: WasmPtr<u8>,
    buf_len: __wasi_size_t,
    cookie: __wasi_dircookie_t,
    bufused_ptr: WasmPtr<__wasi_size_t>,
) -> Result<(), Errno>