fix(#1193): render multiple relations

[fgrandel]

📑 Summary

Resolves #1193

📏 Design Decisions

In graphlib edges have an ID that is constructed from the nodes being linked plus an (optional) name. If two edges are provided with the same nodes and name (or no name at all) then they overwrite each other. Mermaid's class diagram parser already collected the relations correctly but added them without name. I'm now using the relation label as a natural choice for the edges name. This fixes the problem.

📋 Tasks

Make sure you

• 📖 have read the contribution guidelines
• 💻 have added unit/e2e tests (if appropriate)
• 🔖 targeted develop branch

[callaertanthony]

Hi !
It seems that the solution provided only resolves Class Diagram, is it possible to also consider State Diagram ?
This would offer the possibility for a state to have multiple transitions for a same sink.

stateDiagram
	State1 --> State2 : transition1
	State1 --> State2 : transition2

[jgreywolf]

Just a note - when there is more than one relation the relation text overlaps each other making it hard to read. I believe that this has more to do with positioning and overlap for class diagrams in general, and since there are already a couple of open issues on those not going to hold this one