Archiving the XAML Standard Repo

[timheuer]

As mentioned in an update to the README last year and repeating here, we're going to archive this repo effective immediately.

The focus of aligning the XAML dialect across a number of our XAML-based languages was our initial goal. We were unable to find a direct alignment with our product areas as we’d hoped. To that end, we are choosing to archive this repo. Our frameworks such as Windows Presentation Foundation (WPF), WinAppSDK, and .NET MAUI are rich with features powerful for each use case and can leverage XAML declarative markup unique to their own scenarios and underlying platforms they serve. We will continue to evolve those frameworks as appropriate, enabling developers choosing those platforms for their apps to be most successful in their developer scenarios and targets.

As a side note, the issues will remain in their current state as we're not resolving/dispositioning any of them individually as a part of this archive.