[php-src] PR #24248: Fix GH-21992: symlink() creates link at dangling symlink target

Pull Request: https://github.com/php/php-src/pull/24248 Author: bukka Fixes #21992. expand_filepath() resolves the last component of the link path, so when it is an existing dangling symlink, the new link is silently created at the symlink target and symlink() returns true. link() has the same problem. This resolves only the directory part of the link path and keeps the last component as given, so the kernel reports EEXIST for any existing entry (including a dangling symlink) and the usual "File exists" warning is emitted. No extra pre-check is needed, so there is no race between the check and the link creation. Supersedes #22024, which added an lstat/stat pre-check instead of fixing the path resolution and did not cover link().