Named Avalonia colors: an example of listing and sorting them by color channel

[h0lg]

Adds a small sample program to list and sort named Avalonia UI colors by different color channels (R/G/B/A, H/S/V, H/S/L).
I originally built this as a tool for prototyping control colors during theming - namely finding color examples of a certain hue or brightness range. E.g. finding a matching bright text color for a dark background and vice versa.

It poses the question how to create empty horizontal WrapPanels for .itemsPanel() extensions and proposes a solution (see EmptyWrapPanelBuilders).

I've included it on the Color Picker page of the Gallery, although it strictly isn't a color picker widget in the same sense.
If you find it a useful example, you may alternatively or additionally include it as an example for several other widgets it showcases:

• horizontal ListBox
• horizontal ItemsControl
• lazy-loaded Expander
• WrapPanel
• ThemeAware

[edgarfgp]

Thanks for creating this nice sample. Just added couple suggestions.