bug#63956: 29.0.91; tex-mode display problem in emacs-29

[Jeff Norden <norden.jeff@gmail.com>]

I've been trying out the 2nd emacs-29 pretest.  It seems great.
I haven't needed to tweak a single line of my .emacs or any of the
custom files it loads (about 1200 lines in all).  The new
'with-restriction' feature may simplify a project that I've been
playing with for a while.

However, I have found a minor issue with a change made to tex-mode.
The simple calls to `display-buffer' in tex-mode.el have been replaced
with:
    (display-buffer tex-shell display-comint-buffer-action)
The default value for display-comint-buffer-action is set from
display-buffer--same-window-action.

As a result, the default behavior of `tex-buffer' or `tex-region' is
that the document you are editing *disappears*, and and the window it
was displayed in shows just the error messages (or lack thereof) from
running TeX.  You then need to switch back to the document's buffer to
continue editing.  This behavior makes no sense.  It would be
equivalent to running `compile' on a C file, and then only seeing the
output from make/gcc/etc, with the source code hidden.  The correct
behavior in both cases is to show the process output in a window
alongside the source.  Anyone who has been using tex-mode for years
would certainly find this new behavior disruptive, although it is
easily corrected.

I'm not sure if the `display-buffer' calls in tex-mode.el need to have
an action argument, but if they do, it should be similar to what is
used in compile.el.  I'll be the first to admit that I'm not
particularly well-versed in the current intricacies of buffer display
actions (nor do I have any real desire to become so :-).

Thanks,
-Jeff