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)

Comienza leyendo los issues relacionados #2462 y #2459; después, examina el nodo Math existente y cómo exponen variables los nodos. Para darlo por terminado, se necesitaría un nodo de geometría para ecuaciones paramétricas con densidad de puntos configurable, un multiplicador de densidad para el renderizado de exportación y un enfoque claro para las ecuaciones con distintos números de variables.

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