xfs_scrub: add a couple of omitted invisible code points

xfs_scrub: add a couple of omitted invisible code points

I missed a few non-rendering code points in the "zero width"
classification code.  Add them now, and sort the list.  Finding them is
an annoyingly manual process because there are various code points that
are not supposed to affect the rendering of a string of text but are not
explicitly named as such.  There are other code points that, when
surrounded by code points from the same chart, actually /do/ affect the
rendering.

IOWs, the only way to figure this out is to grep the likely code points
and then go figure out how each of them render by reading the Unicode
spec or trying it.

$ wget https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
$ grep -E '(separator|zero width|invisible|joiner|application)' -i UnicodeData.txt

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>