This includes `std::os::darwin::fs`, which is re-exported under
`std::os::macos::fs` and `std::os::ios::fs`.
`std::os::darwin::raw` is not exposed, which means that
`MetadataExt::as_raw_stat` isn't available on tvOS, visionOS and
watchOS.
The functionality available on Apple platforms are very similar, and
were duplicated for each platform.
Additionally, this fixes a warning when compiling the standard library
for tvOS, watchOS and visionOS by marking the corresponding code as
dead code.
