This is a followup of
MDL-61393, where, after asking both @ dev chat and between integrators, it was decided that it was enough to provide .svg icons only.
That conclusion immediately means that there won't be other formats (png, gif...) for some of the icons and, also, that the svg2png fallback won't work for an increasing number of icons.
So this issue is about to decide what to do both with:
A) icons in those non-svg formats and,
B) any fallback or support to those formats.