PR Summary

We should allow users to center markers by center of mass. This is the code to compute the center of mass of an arbitrary path (treats paths of different intrinsic dimension correctly).

Roadmap:

#16812 (*) <-#16832 (*) <-#16859 (*) <-#16888 (*) <- (This PR) (*) <-#16891 (MarkerStyle improvements!)

"<-" means "depends on", and "(*)" marks PRs whose implementations are complete and fully ready for review.

PR Checklist

• Has Pytest style unit tests
• Code isFlake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way