Default ambientMaterial to the base material color if unspecified

[davepagurek]

Resolves #6125

Changes

• In Feature Implemeted -- Multiple Material support for geometry #5774, we updated p5's material model to be a bit more like Processing's, where one can specify a separate color for the ambient, specular, and emissive components of the material
• Unlike in processing, the p5 implementation required all components to be set separately
  • This meant that previous code that only specified, for example, fill(), would look different due to the ambient component remaining at a default value
• In Processing, the ambient color defaults to the same color as the specular color or fill if left unspecified
• This PR updates the p5 implementation to match Processing:
  • If you only specify the specular color or fill, it will be used for the ambient color too
  • Otherwise, your explicitly set ambient color will be used

Screenshots of the change

//v1.4.2 fill('red')	//v1.6.0 fill('red')	//updated fill('red')	//updated fill('red') // Explicitly specified white // ambient material ambientMaterial(255, 255, 255)

PR Checklist

• npm run lint passes
• [Inline documentation] is included / updated
• [Unit tests] are included / updated