Fix Sourcegraph with MR diffs

• Step 1: Setup fake web worker for jest
• Step 2: Fix Sourcegraph with MR diffs
• Upstream PR: Update GitLab domFunctions to use new interop

What does this MR do?

This MR is part of fixing Sourcegraph for Merge Request diffs. It does this in two commits:

1. Establish tests for interoperability. These tests use Sourcegraphs current way of querying for line metadata. This reveals a bug since the tests are not passing.
2. Fix the way we expose line metadata and change how Sourcegraph should be querying for this.

We will follow-up this MR with an upstream Sourcegraph MR.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #296769 (closed)