Prevent any `Link` or `SymbolicLink` entry from being created if its
`linkpath` would target a location that is through a symbolic link from
the current working directory.

This matches the behavior of `bsdtar` for hard links, and is somewhat
more restrictive in applying the same logic to symbolic links as well.

Unpacking links with targets that extend through symlink folders is
allowed if `preservePaths` option is enabled, as this disables all
protective link checking by design, and is only designed for use with
trusted input.

Fix: GHSA-83g3-92jg-28cx

UnpackSync[ENSURE_NO_SYMLINK] previously constructed SymlinkError's
"into" path using the full original linkpath parts array, which could
produce misleading diagnostics.

Build the "into" path from the original `cwd` value and the `parts`
list.

Fix: GHSA-qffp-2rhf-9h96