Adopt to pre-release extension support

[Isidor Nikolic]

Hi VS Code PM here 👋

Refs: microsoft/vscode#15756

VS Code now supports pre-release extensions. Docs that should help: https://code.visualstudio.com/api/working-with-extensions/publishing-extension#prerelease-extensions

I know vuedx has a separate Insiders extension. Ideally you would adopt to our pre-release support and we would deprecate that other extension. VS Code can automatically migrate your existing vuedx Insiders users to the pre-release version of the extension once you have done the adoption.

Let me know what you think