Add browser extension functionality if possible

[TheWebTech]

Adding web extension support would enable the extension to work in github.dev as well as vscode.dev, as well as potentially other VS Code based code editors like gitpod and possibly codeanywhere.

There certainly may be some functionality that wouldn't be supported in the web extension version. But a lot of it likely will work.

https://code.visualstudio.com/api/extension-guides/web-extensions#update-existing-extensions-to-web-extensions