Fix browser extension end-to-end tests
Created by: marekweb
This fixes:
- The "open on Sourcegraph" button test
- It now opens a new tab, so the test now expects a new page with the destination URL
- The tab needs to be active for the test to run, but the new install opens up automatically, so the test now explicitly focuses the tab.
- Hover tests and go-to-definition
- Update two DOM line IDs used for hovering on GitHub
- Also explicitly focus the tab
Final update
This PR fixed the GitHub tests, but not the GitLab tests.