bug#69992: Minor improvement to image map transformation logic

[Joseph Turner via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

David Ponce <da_vid@orange.fr> writes:

> Here is my last patch. The only change compared to the previous patch is that
> now the scale factor is correctly calculated based on the size of the image and
> the displayed size. To minimize the performance impact, I saved a call to
> `image-size' by doing the calculation directly in the `image--compute-map' and
> `image--compute-original-map' functions. I did some benchmarks and the
> difference is not significant. The tests still give the same results :-)

Thank you for these fixes and optimizations!!! The tests pass for me.

> Here is the new change log:
>
> 2024-03-30  David Ponce  <da_vid@orange.fr>
>
> 	* lisp/image.el (image--compute-rotation): New function.
> 	(image--compute-map, image--compute-original-map): Use it.
> 	Ensure all transformations are applied or undone according to what
> 	Emacs does internally.  Call a transformation function only when
> 	needed.  Fix doc string.

With this fix, I think we can remove `image-tests--map-equal'. I'll
submit a new bug.

> 	(image--scale-map): Assume effective scale argument.
> 	(image--rotate-map): Assume effective rotation argument.
> 	(image--rotate-coord): Improve doc string.
> 	(image--flip-map): Remove no more used flip argument.
>
> 	* test/lisp/image-tests.el (image-create-image-with-map): Use a
> 	valid SVG image otherwise `image-size' will not return a valid
> 	value and calculation of scale could fail.
> 	(image-transform-map): Update according to changed signature of
> 	image--flip-map.
>
> Thanks!
>
> [2. text/x-patch; image-compute-map-V2.patch]...