misc: amend unicode confusing name tests to check for hidden tag characters

misc: amend unicode confusing name tests to check for hidden tag characters

The Unicode consortium has twice defined (and later deprecated) special
"tag" codepoints.  These tag codepoints are not supposed to be rendered
(i.e. they're invisible) but you can certainly encode them in
directories and labels to try to confuse users.

xfs_scrub already knows how complain about these tag characters because
libicu can detect both their presence and their use in confusing name
attacks, so add this as an explicit regression test.

Link: https://embracethered.com/blog/posts/2024/hiding-and-finding-text-with-unicode-tags/
Link: https://arstechnica.com/security/2024/10/ai-chatbots-can-read-and-write-invisible-text-creating-an-ideal-covert-channel/
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>