More an more, extension authors are providing a nightly/insiders version of their extensions. Which can cause issues for end-users if they have both versions installed. And today, extension authors can't properly deal with this because of the static contributions -- which can cause a bad end-user experience.

Since we have a preview flag in package.json, I would propose that we add a new previewOf option that could be set to an extension id, that this preview is a preview of. So for example, GitLens Insiders (eamodio.gitlens-insiders) would set "previewOf": "eamodio.gitlens".

When VS Code sees this flag, it would determine if the previewOf extension is installed and enabled, and if so, then would auto-disable this extension so it wouldn't be activated at all.

This would avoid a bad end-user experience, especially if we show a reason in the extension view to why this extension is now disabled. It would also avoid issues with Codespaces issues with built-in extensions and nightlies.

/cc @jrieken @sandy081 @connor4312 @RMacfarlane @JacksonKearl