Image formatter to expose image width and height

ok, implemented this.

The MR now:
* Exposes the image formatter with a proper label, so it is easily discovered. I had missed that "file properties" is handling images!
* Works over the existing formatter to improve it.
* It now adds width/height correctly from the image style. Tested and verified to work with focal-scale and normal scaling correctly.
* It makes flattening optional
* It now also implements adding it as slot (even though this does not make sense always, it now works as configured)
* it optionally removes flattening-prefix, since the prefix is not needed when the image is within a media entity. so there can be a nice output easily then
* adds test coverage for everything, co-authored by copilot. Code is not 100% nice all the time, but it tests things correctly!

Thank you, merged then!

Automatically closed - issue fixed for 2 weeks with no activity.