Multiline does not support sortPoints

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Now that it supports intersect, this would be very useful.

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Note that Ray does not support this either, which makes sense. In the context of a Multiline, if there is just one ray and no other shape, I suppose this method should throw. But if there are two rays (on both ends), or a single ray and arcs/segments, then it is valid to order points along them.

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FWIW the algorithm I am working on no longer requires sorting points. So feel free to close this if you don’t consider it important. I also realized that a multiline can cross itself, which makes this tricky: should the points be sorted according to their first appearance, or should some points appear more than once in the returned array?