[Feature] Create a version of toolkit for WinUI 3

[ranjeshj]

See the Preview Bits on #3295

Original Request by @ranjeshj:

Toolkit cannot be used with WinUI3 until we have a version of the toolkit for WinUI3.
issue moved from microsoft ui xaml repo - microsoft/microsoft-ui-xaml#1860

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Info from Toolkit Team

WinUI3 changes the default namespace of all components from Windows.UI.Xaml to Microsoft.UI.Xaml, this means all libraries also need to reference WinUI 3 to share the base components as building blocks for the UI Stack (like DependencyObject, FrameworkElement, UIElement, etc...).

In order for the Windows Community Toolkit to be compatible, we need to adopt not only our own components but ensure any UI dependencies we have adopt WinUI 3 as well.

• Main Packages
  • 1. Microsoft.Xaml.Behaviors.Uwp.Managed (see their Issue 147)
  • 2. Win2D (have reached out to team, see their Issue 707)
  • 3. ColorCode.Uwp (test PR here, only used by MarkdownTextBlock which we plan to split to separate package for 7.0 see Issue [Future] 7.0 Release Plan #3062)
• Sample App:
  • NotificationVisualizer (have reached out to team)
  • Monaco Editor UWP (Have POC but need improvements to WebView2 for practicality).
  • Graph-Controls (this is our own toolkit work, need tracking item at https://aka.ms/wgt)

[ghost]

Thanks for submitting a new feature request! I've automatically added a vote 👍 reaction to help get things started. Other community members can vote to help us prioritize this feature in the future!

[azchohfi]

We have a branch that has that (https://github.com/windows-toolkit/WindowsCommunityToolkit/tree/winui), but it's definitely not fully supported yet. You can play around with it and the build system should just work.

[michael-hawker]

I've created a WinUI3 milestone for us to track any work that has a dependency on WinUI.