Geometry_Engine: Split and OutlineFromLines methods could be extended to PolyCurves

#### Description:

I believe the currently applied algorithm of turning lines into outlines could be leveraged for nonlinear curves too by splitting them with each other first, then turning into a graph and processing it in the same way as in the method for lines. Once this is done, `Split` should be able to leverage it almost without any rework.

Not requested by anyone so no priority, leaving it here for future reference.