bug#70399: ConTeXT options need updating

[Jim]

Emacs  : GNU Emacs 27.2 (build 1, x86_64-slackware-linux-gnu, GTK+ Version 
3.24.27) of 2021-03-25
Package: 14.0.3.2024-03-17

Some of the ConTeXt-specific features are a bit outdated, and, as of
recently, arguably broken.

(1) TeX-command-list contains the following
    ("ConTeXt" "%(cntxcom) --once --texutil %(extraopts) %(execopts)%t"
    and --texutil isn't in texlive 2023's context, texlive 2024's context,
    or the context in the ConTeXt distribution.

(2) A recent change (early April 2024?) to context has changed how
    synctex is done.
    On the good side, with the right option context will produce a
    synctex file that epdfinfo knows how to parse.
    On the bad side,
    (a) rather than calling with "--synctex=1" (as done in
        ConTeXt-expand-options in context.el) the correct option is now
        "--synctex=repeat";
    (b) but if context is called with "--nonstopmode" (or "--nonstop")
        the "--synctex=..." request to create a synctex file is over-ridden.
    It is easy for a user who knows what is going on to use
        (setq ConTeXt-texexec-option-nonstop "")
    but changing --synctex=1 to --synctex=repeat seems to require
    a redefinition of the function.

The --synctex=repeat version may not have reached texlive 2024 yet, but
using --synctex=repeat with the version of context in TL2024 creates the
same synctex file as --synctex=1, so there seems to be no harm in
changing this.

In case it wasn't clear:
What I expected to happen:
        running context would create a synctex file.
What happened (with new context):
        the synctex file was not created.

Thanks.

                                Jim

Bonus "bug": TeX-submit-bug-report suggests upgrading to the version from
https://www.gnu.org/software/auctex, but as of today that would be a
downgrade, since it says the current auctex version is 13.3.