Add node that plots graphs as geometry using parametric equations

I wanted to draw this illustration using graphite, but ended up using desmos and screenshotting it, because they support parametric equations. It will be nice to have such a node.

Desmos illustration

I think that in this node we should be able to specify density of the geometry (amount of points), because different equations require different density, and it can affect performance.

I think there also should be density multiplier for the export rendering (if there is such a regime). So that at the editing stage we may see segmented geometry, and for the final render it will be smooth.

Also, unsolved problem: how to make this node accept any amount of variables (so that you can tweak behavior of your equation, like `l` in my example). This is also the problem for the Math node. Without this, this node will be not as useful is it might be. (#2462, and see also #2459)