Replace fn with direct downloadFile import to fix issue where fn was not found

[acgillette]

Resolves #7905

Changes:
Change the p5.Geometry file to import downloadFile directly and call it rather than relying on fn, which was returning undefined. Also updated the stlSave function and tested that it worked.

Wasn't sure if the fn in the geometry function was needed so left it. Also wasn't sure if unit tests should be added, so I left as is for the moment.

PR Checklist

• npm run lint passes
• Inline reference is included / updated
• Unit tests are included / updated

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Thank You!

[davepagurek]

lgtm, thanks for taking this on!

[davepagurek]

@all-contributors please add @acgillette for code

[allcontributors]

@davepagurek

I've put up a pull request to add @acgillette! 🎉