add DensifyHaversine trait

[JosiahParry]

• [x] I agree to follow the project's code of conduct.

• [x] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

This PR adds a DensifyHaversine trait which enables users to densify line based spherical geometries.

It provides the ground work for enabling linestring segmentation on geographical coordinates which can be used by downstream libraries such as stplanr.

[michaelkirk]

re: the CI failure - You might want to check out our usage of approx elsewhere for the sloppy floating point matching.

[JosiahParry]

Oh thank goodness. That was an adventure!