Validates if the given input is a symbolic link.
v::symbolicLink()->assert('/path/to/symbolic-link');
// Validation passes successfully
v::symbolicLink()->assert(new SplFileInfo('/path/to/file'));
// → `SplFileInfo { __toString() => "/path/to/file" }` must be an accessible existing symbolic link
v::symbolicLink()->assert(new SplFileObject('/path/to/file'));
// → `SplFileObject { current() => "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque nec enim vitae ve ... }` must be an accessible existing symbolic link