Alias GLSL's mix function as lerp in p5.strands (#7875)

[LalitNarayanYadav]

Resolves #7875

Changes:

• Introduced an alias for the GLSL mix function under the name lerp in p5.strands.
• Ensures that lerp() within p5.strands maps to mix() when generating shader expressions.
• Falls back to the original p5.js lerp() function outside of p5.strands.

Rationale:

This change bridges the gap between core p5.js and p5.strands by making lerp() work seamlessly within shader code. It increases accessibility by allowing familiar p5.js functions to be used in new contexts.

A short inline comment was also added for clarity:

PR Checklist

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

[LalitNarayanYadav]

fixes #7875

[lukeplowden]

Thank you Lalit for working on this! I've left a couple of suggestions. What was causing a reference error, however? I can't recreate it. If you could let me know a bit about your dev environment that might help. How are you building the library or importing this module?

[LalitNarayanYadav]

I was using VS Code but the issue I was facing was not because of environment. I had created a syntax error by mistake which I was not noticing.

[lukeplowden]

Thank you, almost there! Could you also remove the unused variable fn on line 11?

[LalitNarayanYadav]

I have made the changes as you suggested. Please review it when you have time.