TODOs:
* path_filestat_set_times, fd_filestat_set_times: different types used to set
  times for a Dir vs a File, this is a fs_set_times vs cap_fs_ext divergence
* File::set_fdflags is unimplemented, File::get_fdflags is lying - these are
  fcntl on unix, reopenfile / ?? on windows. Not implemented in system-interface yet.
* async scheduling!


wasi_tests::path_link
    - need DirExt::hard_link that follows symlinks.
wasi_tests::path_rename_trailing_slashes
    - trailing slash behavior of files is wrong: trailing slashes are ignored,
      should cause an error.
wasi_tests::remove_directory_trailing_slashes
    - cap-std Dir::remove_dir gives EINVAL when trying to remove dir with
      trailing slash. otherwise, everything passes.

wasi_tests::fd_flags_set
    - set_fdflags is not implemented. test wanted to clear O_APPEND mode
wasi_tests::path_filestat
    - fdstat.fs_flags is not populated correctly - APPEND | SYNC aren't
      present because File::get_fdflags isnt implemented correctly


wasi_tests::poll_oneoff
    - no sched yet
wasi_tests::sched_yield
    - no sched yet