Rework automatic theming

[passsy]

The automatic theming of Wiredash (using Wiredash.of(context).show(inheritMaterialTheme: true)) has been reworked. It worked for the most part, but some colors did not generate good secondary colors and colors like the appHandleBackgroundColor were not customizable.

The new auto-theme uses the material_color_utilities under the hood, which uses an interesting color space to generate matching color tones in different shades, exactly what Wiredash needed. More on this on https://m3.material.io/styles/color/dynamic-color/overview

It also adds new custom colors:

• primaryContainerColor
• textOnPrimaryContainerColor (replaces primaryTextColor)
• secondaryContainerColor
• textOnSecondaryContainerColor (replaces secondaryTextColor)
• appBackgroundColor
• appHandleBackgroundColor

To test the whole thing I created a Theme customizer example/lib/main_customizer.dart to test out different colors in light and dark mode. That's not the final design, but functional.