Fix: restore lerp alias to GLSL mix in p5.strands

[aashu2006]

Resolves #8646

Changes:

• Fixes lerp() not working in p5.strands
• Maps lerp to GLSL mix inside a Strands context
• Falls back to normal p5.js lerp() outside

This was previously implemented in #7875 but got lost during refactoring.

Screenshots of the change:

• The visual tests show lerp() and mix() giving the same output in p5.strands

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@523cc74/lib/p5.min.js

Published Packages

• https://pkg.pr.new/p5@523cc74

Commit hash: 9b8a527

Previous deployments

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[perminder-17]

Looks good to me!