Update VSCode instructions

[stefnotch]

https://docs.flaxengine.com/manual/scripting/debugging/visual-studio-code.html is outdated, since Microsoft is working on some new C# extensions

• https://marketplace.visualstudio.com/items?itemName=ms-dotnettools.csharp is the basic one.
• https://marketplace.visualstudio.com/items?itemName=ms-dotnettools.csdevkit is the more advanced one. Do note that the C# dev kit has some special licensing stuff. That should probably be briefly mentioned in the updated documentation.

C# Dev Kit builds on the same foundations as Visual Studio for some of its functionality, it uses the same license model as Visual Studio. This means it's free for individuals, as well as academia and open-source development, the same terms that apply to Visual Studio Community. For organizations, the C# Dev Kit is included with Visual Studio Professional and Enterprise subscriptions, as well as GitHub Codespaces. For full terms and details see the license terms.