ert-font-lock improvements

[Vladimir Kazanov]

Hi all,

Some time ago an extension for ERT (the built-in unit testing system)
was merged: ert-font-lock, a tool for syntax highlighting tests.

A couple of weeks ago certain problems (see bug#69714) with
ert-font-lcok were raised, and I've also accumulated a few
quality-of-life improvements for the tool.

Could somebody please take a look at the patch and merge it if it's
okay? Bug author and myself did some testing and the changes proposed
do solve a lot of problems for us.

Thanks,
Vlad

--
Regards,

Vladimir Kazanov