* add a wasi-test to show a dir_fd always gets ERRNO_BADF on appropriate fd_ operations.
This is a conformance test for the current behavior of preview 1 in wasi-common. It is debatable whether this is the right errno, I think for most of these ERRNO_ISDIR would be more descriptive, but this is the behavior we have.
* Add comments to all the fd op failures explaining closest linux/posix behavior