According to the GNU cp official documentation[1], a symlink is only
created if all source paths are absolute, unless the destination files
are in the current directory.

This fix solves this GNU cp incompatibility by:
- Adding verifications when handling symlinks, to ensure that a symlink
  with relative path are only created if the destination is within the
  current directory.
- Adding unit tests to cover this modifications, and ensure the behavior
  is correctly align with GNU documentation.

[1]:
https://www.gnu.org/software/coreutils/manual/html_node/cp-invocation.html#index-_002ds-16

Due to the nature of Windows using backslash instead of regular slash to
separate the directories, the test would fail because it was using a
hardcoded output. To address that was changed the method to evaluate the
output to a more flexible one, that way the backslash would not be a
problem.