the fdstat of a dirfd needs to include both the file and dir rights in
the inheriting field.
The wasi-libc path_open bases the base rights of child directories off
the inheriting rights of the parent, so if we only put file rights in
there, opening a child directory will not have any directory operations
permitted.
Fixes https://github.com/bytecodealliance/wasmtime/issues/2638
c9d8ed03c9