Enable dark mode for doxygen \image

[friedrichatgc]

Doxygen can add custom images to the documentation using the \image command. The css is extended to enable dark mode for such images, like already done for the "dot" generated SVG inheritance diagrams.

(Tested only with SVG images defined using the \image command)

[jothepro]

Can you elaborate on how you would use this in practice? At a first glance I don't think it's a good idea to invert all images in a documentation by default.

In the demo page I explicitly marked any image that can be inverted without looking awkward with a custom class. Would this also work for you?

Also, there is an open issue & PR about adding support for the <picture> HTML-tag to Doxygen, which would allow providing separate images for both light & dark mode.

[friedrichatgc]

My plan was to enable this only for SVG (which are mostly used for line drawings where color inversion for dark mode makes a lot sense). SVG is added by doxygen using the