egui_plots: simplifying (complex) lines with Ramer–Douglas–Peucker might save a lot of triangulation/overdraw time

A [HN commenter](https://news.ycombinator.com/item?id=39371026) suggested looking at the Ramer–Douglas–Peucker polyline simplification algorithm. For very big lines that generate lots of triangulation/overdraw load, that might be a very neat optimisation. We'd need to run it with e.g. 0.1px tolerance, and cache the result against the zoom level.