Problem

Taken from #19591 (comment).

There are cases in which one may want the legend items to be drawn in reverse oder.

Proposed solution

Add a parameter reverse to Legend.

Implementation-wise this should be as simple as reversing

In this simple form, reverse would be a creation-time setting, which could not be changed afterwards. But I think this is ok for now. Reversing at runtime would need a bit more code restructuring.