Add support for SVG animations

[Trombach]

Description

Implementation PR: vtbag/element-crossing#5

Adds an animated SVG image to test and demonstrate the new svg-anim expression

Todo:

• make tests actually useful (not sure how since it's difficult to compare the animation times as they depend a bit on when playwright actually runs the code)
• amend docs with info about abbreviated form, once decided

[martrapp]

Next to the vanilla demo there is also a plain and a over-the-top demo that we should update accordingly by adding the animated SVG.
/crossing/over-the-top/1/
/crossing/plain/1/

[Trombach]

Next to the vanilla demo there is also a plain and a over-the-top demo that we should update accordingly by adding the animated SVG. /crossing/over-the-top/1/ /crossing/plain/1/

Thanks, I missed that. I will add this and also make the required changes once we've agreed on the final implementation for this feature.

[martrapp]

Love it! I'm very happy about this contribution! Thank you very much, Lukas!