Forward fix for wide gamut changes in colors

[gaaclarke]

fixes #9

changes:

• Renames ColorModel.withValues to ColorModel.fromValues
• Renames LabColor.a to LabColor.chromaticityA
• Renames LabColor.b to LabColor.chromaticityB
• Renames OklabColor.a to OklabColor.chromaticityA
• Renames OklabColor.b to OklabColor.chromaticityB
• Adds Color.a, Color.r, Color.g, Color.b, Color.withValues, Color.colorSpace

I chose fromValues instead of withValues since "with*" is used to mean tweaking an existing color, whereas that method is creating completely new color.

[gaaclarke]

friendly ping @james-alex @isaacroberts

[lukemmtt]

FYI, after upgrading my project to the new stable release Flutter 3.27.0, the underlying issue here resulted in build errors in my project. In my tests, @gaaclarke's PR here resolves these errors. Thus, this PR (or another similar fix) needs to be merged to resolve build incompatibilities between color_models and Flutter 3.27.0.

In case it might help anyone in the meantime, I resolved my project's build errors with a dependency override pointing to gaaclarke's PR code (but substituting with my own fork), like so:

dependencies:
  color_models:
    git:
      url: https://github.com/gaaclarke/color_models.git
      ref: wide-gamut
      path: color_models
  flutter_color_models:
    git:
      url: https://github.com/gaaclarke/color_models.git
      ref: wide-gamut
      path: flutter_color_models
      
dependency_overrides:
  color_models:
    git:
      url: https://github.com/gaaclarke/color_models.git
      ref: wide-gamut
      path: color_models
  flutter_color_models:
    git:
      url: https://github.com/gaaclarke/color_models.git
      ref: wide-gamut
      path: flutter_color_models