Make use of SVG graphics

Eclipse added support for SVG images in 2025-06, see https://eclipse.dev/eclipse/markdown/?f=news/4.36/platform.md
AFAIK, we already have the source svg files for some of our used icons in the /svg directory of this repo.
So I think there are a few improvements we can make now:

1. Use the svg files instead of the pre-rendered png where possible
2. Use svg variants of images that we consume from other plugins, i.e., platform:/....
3. Search/obtain svg files for the remaining png files without a source svg. Maybe from https://github.com/eclipse-platform/eclipse.platform.images

I will try to make these changes in a few PRs. (1) and (2) should be straight forward. (3) is probably a bit more difficult.

After we switched to svg, we probably still have to keep the png images around for some time, because other downstream implementations might re-use them. We could probably remove our pngs when the Platform removes theirs, which might happen some time after 2027-06, see https://eclipse.dev/eclipse/markdown/?f=news/4.36/platform.md