feat: Add parabola

[itsCryne]

This would resolve #982

There may still be some rough edges as this is really my first time contributing to a bigger GUI project 😇

Most code of the parabola is based upon the existing rectangle and quadratic bezier shapes.

[flxzt]

Thanks! The code itself looks good, but I don't think we need to introduce a dedicated Parabola Shape. We could use the already existing geometric primitives and the parabola builder could just emit a quadratic bezier curve.

[Doublonmousse]

Wouldn't that (introduce a new shape) be a way to future-proof the implementation if we ever decide that we want to add better editing capacities (like editing the anchor points after the shape is constructed) in the future that are shape-specific ?

Right now this doesn't matter, but it could in the future

[flxzt]

I don't really see the benefit of that. If you want to edit the shape later you could also implement it on the bezier curve, like being able to move the control points. I also want to keep the number of primitives low, otherwise we end up with a new shape for every mathematical function..

Edit: and you can already do that, the parabolic shape is retained when resizing the curve as a selection

[itsCryne]

Sorry for not communicating for so long - I got busy as the summer term started.
I'll try to find some time to change the implementation as suggested above in the next few weeks.