bug#64391: buffer narrowing slowdown regression in emacs 29

[Eli Zaretskii]

> Date: Thu, 06 Jul 2023 17:33:13 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: acohen@ust.hk, 64391@debbugs.gnu.org, mattias.engdegard@gmail.com, 
>     monnier@iro.umontreal.ca
> 
> 
> I pushed a proposed change to the scratch/bug64391 branch.
> 
> It contains three commits:
> 
> - b741dc7fcd which is the minimal possible commit to fix this bug
> 
> - 01fb898420 which moves a few statements from the callee 
> (internal--label-restriction) to its only caller 
> (internal--labeled-narrow-to-region), and simplifies the code accordingly
> 
> - c52ade305e which is optional, and makes the symmetrical change for the 
> widening case

OK, please merge the first two commits to the release branch, and
thanks.