Add support to github.dev/make this a web extension

[LinqLover]

At the moment, in github.dev you cannot enjoy this awesome extension:

This could be fixed by making this extension compatible with the web extension interface:

https://code.visualstudio.com/api/extension-guides/web-extensions

(It's not overly complicated; provided that this extension does not use node-specific features such as fs or external binaries, this looks like only defining an alternative entry point for the web extension.)

[abeatrix]

@LinqLover Thanks for filing the issue! We are happy to announce that Sourcegraph is now a web extension as of v2.0.9.

[LinqLover]

That's awesome news! :rocket:

If I go to <vscode.dev>, install the extension, and press the "Don't have an account?" link, I am redirected to this page:

(https://webviewview-sourcegraph-searchsidebar.vscode-webview.net/)

But when I generate and paste a token manually via https://sourcegraph.com/users/LinqLover/settings/tokens/new, the login works as expected.

Looks very nice, keep up the good work!