Sample options and viewable source

[Arlodotexe]

This PR makes progress towards a more cohesive sample system by adding the infrastructure for sample options and viewing source code.

Overview:

• Adds XamlNamedPropertyRelay to enable accessing XAML declared x:Name properties from outside of a control.
  • This will help create more advanced option panes without cluttering up the code-behind shown to the user.
  • Added under a new project CommunityToolkit.Labs.Core.SourceGenerators.XamlNamedPropertyRelay. Separate as not all projects need this generator.
  • Example can be found in the second placeholder sample.
• Adds generated sample options which automatically generates properties to bind to and a sample page to control them.
  • Supports boolean and multiple choice
  • Example can be found in the first placeholder sample.
• Renames CommunityToolkit.Labs.Core to CommunityToolkit.Labs.Core.SourceGenerators, since it only contains generators and models that use them.
• Includes and displays source code for each sample. Assumes namespace matches folder structure.
• Auto-strips source generator attributes from the final compiled code. Prevents them from showing to the user as code-behind for the sample control.
• Adds source generator diagnostics for usage of attributes that belong to the Labs sample system.
• Adds unit tests for CommunityToolkit.Labs.Core.SourceGenerators, to ensure diagnostics are outputted correctly.

Demo:

Recordedvideo2022-02-07-191730-1.mp4

[michael-hawker]

Haven't dug into the sample display and the markdown renderer stuff yet, but had some initial feedback on the attribute syntax/usage and stuff from the source generator side. Let me know your thoughts and if we can simplify any of those things or not. Also is this just working on UWP or also on WinUI 3/WASM?

[Arlodotexe]

Also is this just working on UWP or also on WinUI 3/WASM?

This should be working on all 3 heads.

[michael-hawker]

@Arlodotexe looking good! Had to clean my local environment to get the WASM head to run.

Only thing is that the XAML/C# display wasn't working there:

I didn't notice any obvious errors or exceptions outputted...

UWP and WinUI 3 heads worked great though!

[michael-hawker]

Looks great, just need to understand the WASM C#/XAML display issue, and we'll be good! 🎉🚀

[Arlodotexe]

For the inconsistent behavior between UWP/WASDK and Uno, I've filed an issue here: unoplatform/uno#8266