Open source contributions are almost impossible

[whiskhub]

I attempted to make an open source contribution for Windows App SDK to address #5335 by opening PR #5726.

However, even for a small change like this one, I encountered several major roadblocks:

• It’s impossible for third-party contributors to build the Windows App SDK (or even just parts of it) locally, due to missing access to the internal-only NuGet repository (NuGet.config#L9).
• There’s no way to trigger the Azure Pipelines (azp run build) in a pull request to check for build failures.
• Even if a build fails, it’s impossible for contributors to view the failure logs to address the issues.
• Pull requests are not proactively monitored; I had to manually ping maintainers to get attention (though I appreciate that my ping was noticed).

This is not just time consuming for third-party contributors, but also the Microsoft employees who need to review such pull requests.

The most important point to improve the situation is being able to build locally. No internal NuGet feeds should be required, at least for local builds.

I hope that with the true open sourcing of the WinUI repository (microsoft/microsoft-ui-xaml#10700), the contributor experience in this repo will be improved as well.