Fixes #2800 - Revamp ColorPicker and Color Scenarios in UICatalog

[tig]

Fixes #2800 - Revamp ColorPicker and Color Scenarios in UICatalog

Depends on #2896

• ColorPicker View let's users pick
  • From the legacy 16-colors
  • From the full palette of 24-bit colors
    • Using RGB
    • Using HSL
• ColorPicker Scenario sufficiently demonstrates all of the above
• True Colors Scenario shows 16-colors correctly
  • When Force16Colors is true

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working