Ensure code intelligence still works on Browser Extensions

Created by: ryankscott

Our current Browser Extensions inject functionality into the code hosts based on the enabled Sourcegraph extensions. For example, if you have enabled the codecov extension, then you will see coverage data in your code host.

As we're sunsetting Sourcegraph extensions we need to ensure that:

• Code intelligence still works with our Browser Extensions.
• We don't break anything for users on older versions of Sourcegraph