Store MarkerRanges in Gitlab::Diff::Line objects [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Contributes to #16950 (closed)

Follow-up for !55669 (merged)

Feature flag #324638

Explanation

I'm making a set of changes to update Gitlab::Diff::Highlight code to make it reusable for word-diff feature.

In the previous MR I created a new MarkerRange class that can keep information not only about the range of changed characters in the diff line but also the type of the change ('addition' or 'deletion').

I updated Gitlab::Diff::Highlight to populate Diff::Line objects with corresponding MarkerRanges. This change should not affect the final highlighted result. I will remove the duplicated code after verifying that the new version works without any problems.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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