seedLink method
Creates a symbolic link at path pointing at target, replacing
whatever sits there.
A target starting with / is absolute; anything else resolves against
the directory holding the link.
Implementation
void seedLink(String path, String target) {
final String normalized = _normalize(path);
_seedAncestorsOf(normalized);
_files.remove(normalized);
_directories.remove(normalized);
final String parent = _parentOf(normalized) ?? _root;
_links[normalized] = target.startsWith('/')
? _normalize(target)
: _normalize('$parent/$target');
}