Override the parallel diff lines property with new data

What does this MR do?

This overrides the parallel diff lines property with the frontend formatted inline diff lines. This is a different approach to adding a new property as it makes the steps to migrate away from these old properties much easier.

Doing it this way pretty much guarantees all existing functionality works as expected as we aren't touching lots of different properties and values.

After the feature has been rolled out we can remove all references to highlighted diff lines and then rename parallel diff lines to a name that is much better suited for its purpose.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• 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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team