bug#47712: 27.1; Provide `string-display-width` function, which takes properties into account, `substring-width`

[Eli Zaretskii]

> Cc: 47712@debbugs.gnu.org
> From: Daniel Mendler <mail@daniel-mendler.de>
> Date: Mon, 12 Apr 2021 15:32:33 +0200
> 
> Okay, fair enough. I am all for removing/obsoleting functionality which 
> is considered an accident as long as a good alternative exists. But if 
> no acceptable alternative exists, the function has a justification and 
> then it may also be possible to improve upon it.

Let's first establish whether indeed there's no alternative.  I'd be
surprised if that's the case, since window-text-pixel-size was written
to support precisely this kind of need.