Implement new edge markers #1271
Description
Reactflow edges have one marker at the beginning of their path and another one at the end.
There are new designs for markers. They also get resized on hover.
Technical challenges:
- Markers are SVG definitions, and are then reused later by the SVG's id. We should make it easy to create all the variants we need.
- As markers are SVG definitions, we must find out how to resize them on hover.