Fix issue in rhumb arc polylines

[dennisadams]

Fixes #8464 .
See my comment over there explaining the issue and the solution.
The issue is actually in all rhumb-arc polylines. This should crush your sancastle with a normalized result is not a number error:

var viewer = new Cesium.Viewer("cesiumContainer");
viewer.entities.add({
  polyline : {
    positions : Cesium.Cartesian3.fromDegreesArray([10.0, 0.0,
                                                    10.0, 5.0]),
    arcType : Cesium.ArcType.RHUMB
  }
});
viewer.zoomTo(viewer.entities);

As I wrote in that comment, I think a better solution would be to compute the number of points for each segment only once and pass it over to generateCartesianRhumbArc. However, I was a bit hesitant to make such a change, because that would break the similarity to generateCartesianArc.
Ideally, I think both generateCartesianArc and generateCartesianRhumbArc can do with some refactoring, for your consideration.

[cesium-concierge]

Thanks for the pull request @dennisadams!

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• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[cesium-concierge]

Thanks again for your contribution @dennisadams!

No one has commented on this pull request in 30 days. Maintainers, can you review, merge or close to keep things tidy?

I'm going to re-bump this in 30 days. If you'd like me to stop, just comment with @cesium-concierge stop. If you want me to start again, just delete the comment.

[hpinkos]

Thanks for the PR @dennisadams. I won't have time to review this before the June release on Monday, but I'll be sure to review this for the July release.

[dennisadams]

Thanks @hpinkos!

[hpinkos]

Thanks for this fix @dennisadams! And thanks for your detailed explanation of the root cause in #8464. That made this really easy to review.

I just added a unit test, and I'll merge this as soon as CI passes