bug#50731: `progress-reporter-update' docstring and `backward-sexp' interaction

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Wed, 22 Sep 2021 15:12:51 -0700
> Cc: 50731@debbugs.gnu.org
> 
> >From my point of view, the first thing to do is to decide is if this
> `backward-sexp' behavior is a bug or not.

How do we decide?  What is TRT for backward-sexp in context that has
no sexps?  If we change anything here, it could potentially affect a
lot of unrelated code out there.

Once again, why does checkdoc want you to have 2 spaces there? what
rule is it that ends up requiring that?