Adds three new system call wrappers for the `symlinkat`, `renameatx_np`,
and `unlinkat` system calls.
### Motivation:
Related to https://github.com/apple/swift-nio/issues/3403 and
https://github.com/apple/swift-nio/pull/3470. This PR adds syscall
wrappers needed to atomically overwrite existing files or symlinks at
the destination during copy operations. On Linux, atomic overwrites
require a "copy to temp file, then rename" strategy. We use the `*at`
family of syscalls (which operate relative to directory file
descriptors) to avoid TOCTOU race conditions.
### Modifications:
1. Adds three system call wrappers for the `symlinkat`, `renameatx_np`,
and `unlinkat` system calls.
2. Adds related tests
3. Updates the `FileSystemError` for `symlink` and `unlink` to take in
the system call name to allow for the `*at` names to be passed.
Add homeDirectory accessor to FileSystem
### Motivation:
Addresses #3381 by adding a `homeDirectory` property to FileSystem,
equivalent to `FileManager.default.homeDirectoryForCurrentUser`.
### Modifications:
- Added `homeDirectory` property to `FileSystemProtocol` and implemented
in `FileSystem`
- Implementation checks `HOME` environment variable first, falls back to
`USERPROFILE` on Windows, or uses `getpwuid_r(3)` on POSIX systems
- Added system call wrappers (`system_getuid`, `libc_getpwuid_r`) with
proper platform guards
- Added `FileSystemError.getpwuid_r()` error helper
### Result:
Users can now access the home directory via `FileSystem.homeDirectory`,
returning a `FilePath` asynchronously. Follows the same pattern as
`currentWorkingDirectory` and `temporaryDirectory`.
Co-authored-by: Cory Benfield <lukasa@apple.com>
Motivation:
We accidentally removed the 'NIOFileSystem' module from the
'_NIOFileSystem' product in the last release.
Modifications:
- Rename 'NIOFileSystem' and 'NIOFileSystemFoundationCompat' to 'NIOFS'
and 'NIOFSFoundationCompat'
- Add back 'NIOFileSystem' which re-exports '_NIOFileSystem' (there was
no publicly available 'NIOFileSystemFoundationCompat' module to
remove, only '_NIOFileSystemFoundationCompat').
Result:
Fewer breaks
Stepan Ulyanin
Karan Lokchandani
George Barnett