VSCode adds support for offline extension installation

[Gijsreyn]

Description of the new feature / enhancement

The new VSCode Insiders support the ability to download and install from .vsix. In December, this will be added to VSCode stable.

For isolated environments, it would be awesome to add offline extension installations.

Note

Asked on VSCode repository to add support on the command-line. Issue in this link for tracking.

Proposed technical implementation details

No response

[Gijsreyn]

@denelon FYI.