Ability to select line numbers + fix Code Intelligence

What does this MR do and why?

Adds the ability to select line numbers with the refactored blob viewer.

Changes in this MR also ensure backward compatibility for things like Code Intelligence and Sourcegraph by adding the required selectors to the highlighted content.

Note, changes in this MR are behind the :refactor_blob_viewer and :highlight_js feature flags.

Screenshots or screen recordings

before	after

How to set up and validate locally

1. Enable the Blob Viewer Refactor feature flag

Feature.enable(:refactor_blob_viewer)

2. Enable the Highlight.js feature flag

Feature.enable(:highlight_js)

3. Open a source file

4. Click on a line number

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.