Make line shader hooks use unmultiplied alpha

[davepagurek]

Resolves #8786

Changes:

• Updates the WebGL line shader to accept unmultiplied color input and expect unmultiplied color output to be consistent with all the other hooks

PR Checklist

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

[p5-bot]

Continuous Release

CDN link

• https://raw.esm.sh/pr/p5@266f1aa/lib/p5.min.js

Published Packages

• https://pkg.pr.new/p5@266f1aa

Commit hash: 0dfed2b

Previous deployments

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