filesystem: a dangling symlink is reported as "Parent directory does not exist" #5191

Problem

When the requested path is a symlink whose target does not exist, fs.realpath in validatePath (src/filesystem/lib.ts) fails with ENOENT and the code falls through to resolveUnicodeEquivalentPath, whose own realpath of the entry fails as well. validatePath reports that as "Parent directory does not exist:

Expected

The error says the path is a broken symlink. Refusing the request is correct and stays.

Prior work

• fix(filesystem): name a broken symlink instead of blaming its parent #4915 by @v0ropaev

The PR(s) above targeted the pre-refactor code and are closed as part of the backlog triage in #4875; this issue is where the work continues, with the PR(s) as a prototype. Thank you to their authors.