Visual studio code has an arm build now [0]. I don't know what regular VS is written on but assuming it's .NET framework I assume a build will show up as the framework itself improves on ARM.
I known in 2010 the Visual Studio UI was rewritten in WPF/CSharp, I don't know which UI system they are using in 2019. It is documented in the wiki entry and a few blog posts MS made.
[0]: https://github.com/VSCodium/vscodium/releases/tag/1.46.1 (basically just MS source minus branding)