bug#53749: 29.0.50; [PATCH] Xref backend for TeX buffers

[Eli Zaretskii]

> Cc: 53749@debbugs.gnu.org, Lars Ingebrigtsen <larsi@gnus.org>
> Date: Wed, 13 Sep 2023 18:23:13 +0300
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> I'm skipping over the etags parser changes (others might comment, I'm 
> just assuming they are good).

They look OK to me at first glance, but we need to make sure the etags
tests still succeed after this change, and the new option should be
documented in the man page.  Bonus points for adding to the etags test
suite a test where this option is activated.