VS Code DSCv3 completion provider

[anmenaga]

PR Summary

This is a prototype DSCv3 VS Code extension that provides completions for classic PS-class-based DSC resources when authoring *.dsc.yaml configuration files.

Completions are displayed when type: is typed in a *.dsc.yaml files. This requires latest dsc build from main branch and relies on PS Adapter cache, which can be generated by dsc resource list * -a Microsoft.DSC/PowerShell.

https://github.com/PowerShell/DSC/assets/11860095/ec88ddb8-6296-4120-9c46-7748ef4a337c