bug#69992: Minor improvement to image map transformation logic

[Eli Zaretskii]

> Date: Wed, 27 Mar 2024 12:16:11 +0100
> From:  David Ponce via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Many thanks for this feature, which is particularly useful to
> automatically recalculate the map of computed images like SVG.
> 
> To make the code faster, by avoiding multiple scans of the map for
> copy and parsing, I propose the following patch which factors most of
> the code into the functions `image--compute-map' and `image--compute
> -original-map'. I have done some tests on my side which are
> conclusive.
> 
> Furthermore, I wonder if the term :base-map would not be more
> descriptive than :original-map?

Thanks.

Joseph, any comments or suggestions?