Add `TriangulateEarcut` algorithm.

[frewsxcv]

• [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.

https://github.com/georust/geo/issues/1002

[frewsxcv]

bors r=michaelkirk

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• ci result