Use random() more in p5.strands examples

Increasing access

Previously, we didn't have random() supported, so many examples use noise() as a source of randomness. This works, but is a little less familiar from how one would use p5 outside of strands, so switching to random() makes these examples a little easier to understand.

Most appropriate sub-area of p5.js?

• Accessibility
• Color
• Core/Environment/Rendering
• Data
• DOM
• Events
• Image
• IO
• Math
• Typography
• Utilities
• WebGL
• Build process
• Unit testing
• Internationalization
• Friendly errors
• Other (specify if possible)

Feature enhancement details

e.g. in the second example in https://beta.p5js.org/reference/p5/buildStrokeShader/, it uses noise for dithering. We probably need to look through all the strands reference items to get a full list of what might need to be updated.