color library Null safety

Based on the Color class in the Flutter SDK.

Since we can't look up the ThemeData class in the build method there are helpful methods to get the design tokens for Material 3 colors.

- Theme.of(context).textTheme.colorScheme.primary;
+ Color.primary();

Classes

BackgroundColor
Color
ColorAlphaBlend
ColorARGB
ColorRGBO
ErrorColor
ErrorContainerColor
InversePrimaryColor
InverseSurfaceColor
MaterialAccentColor
MaterialColor
OnBackgroundColor
OnErrorColor
OnErrorContainerColor
OnInverseSurfaceColor
OnPrimaryColor
OnPrimaryContainerColor
OnSecondaryColor
OnSecondaryContainerColor
OnSurfaceColor
OnSurfaceVariantColor
OnTertiaryColor
OnTertiaryContainerColor
OutlineColor
OutlineVariantColor
PrimaryColor
PrimaryContainerColor
ScrimColor
SecondaryColor
SecondaryContainerColor
ShadowColor
SurfaceColor
SurfaceTintColor
SurfaceVariantColor
TertiaryColor
TertiaryContainerColor