Ensure VS Code extension runs on the web

Created by: tjkandala

Ensure that the VS Code extension can run as a web extension (outlined here).

Most of the work here involves our code sharing features, which depend on git. Search UI, remote browsing, and Sourcegraph extensions do not require any changes to run on the web.

We will first have to get the extension to run on web. We will probably have to output two different main extension bundles: one targeting node, the other targeting WebWorker (main vs browser path in package.json).