More Extension Test/Sample Work

[michael-hawker]

Setup to add back usage of the Extensions in tests via source package helper (test)
Add back some of the removed tests to the test project for extensions Adds nuget.config

Based on updates to submodule here: CommunityToolkit/Tooling-Windows-Submodule#41

Should probably wait to get the sub-module stuff tested and merged and then update in this PR. Probably want to test this PR with and without the new property to test things E2E, initial test is with property as module pipeline should test without.

[michael-hawker]

Oops, guess I hadn't finished and brought the namespace into the XAML, pushed a fix. Hope that's it.

If it all works, then I should spend a bit more time bringing in rest of tests and samples.

Should remove the TODO that ignores the thing about docs needing samples.

[michael-hawker]

I did check the build logs and see that in the tooling module it pulls the extension package from our artifacts feed, but here where we're doing the project reference it doesn't. So, I think we're good on that front!

Should mean that we can use this similar setup now for other packages or the sample app if we need to pull in other Toolkit components, we can test things and iterate as needed in the main repo, and then push to packages for the components to consume via the feed in other repos via the tooling module... FYI @Arlodotexe

Was just a bigger pain in particular here with how ingrained the extensions were and needing to tease out the namespaces to be unified and get to a place where we were good building. Hopefully anything else we start needing isn't as critical and we can bring to be unified first and build on top of that instead.

[michael-hawker]

"D:\a\Windows\Windows\CommunityToolkit.AllComponents.sln" (default target) (1:2) ->
"D:\a\Windows\Windows\tooling\ProjectHeads\AllComponents\Tests.Uwp\CommunityToolkit.Tests.Uwp.csproj" (default target) (11:6) ->
(CoreCompile target) -> 
  D:\a\Windows\Windows\components\Extensions\tests\DispatcherQueueExtensionTests.cs(67,50): error CS[8625](https://github.com/CommunityToolkit/Windows/actions/runs/4615692914/jobs/8159891210?pr=15#step:11:8626): Cannot convert null literal to non-nullable reference type. [D:\a\Windows\Windows\tooling\ProjectHeads\AllComponents\Tests.Uwp\CommunityToolkit.Tests.Uwp.csproj]

[michael-hawker]

Some issues with threading, CI should pass now and tests run.

[michael-hawker]

Let's review and merge this to get everything stable on top of the extensions, and then I can add another PR later as needed to finish samples/tests.