WIP: update to earcut 3.2.3

[mrgreywater]

Work in Progress

Update all changes from earcut.js 3.2.3, including test fixtures
It appears this PR will degrade performance, likely because of many integer<->floating point conversions. Need to investigate.

[mourner]

Ah apologies, I already started a maintenance pass in parallel, but with a different approach - modernizing infrastructure / test setup first, only then moving to porting the actual code changes. Created the PR here #132 — perhaps I could reuse some of your work there?

[mrgreywater]

Oh well, didn't know you already started working on it. I'll stop for now. Take any code you like, maybe I'll look into the performance stuff after you have merged yours ;)

[mourner]

Migration is complete — sorry I didn't warn about it earlier, but having this PR as reference was genuinely useful. I also borrowed a few additions from it (refine result in viz, and tightened warnings). Regression in this PR was indeed due to constant float/int conversion in hot loops, whereas the version in my PR does the double conversion once on input.