Move shared logic into utils

What does this MR do?

For: #236071 (closed)

For: #236075 (closed)

Refactors shared logic between inline and parallel views into a utils file.

NOTE: This is the third of a series of MRs to address the performance issues with merge requests.

👉 We are here

1. Move diff_table_cell logic into inline_diff_row !40906 (merged)
2. Move diff_table_cell logic into parallel_diff_row & remove diff_table_cell
3. 👉 Extract shared logic and duplicated code from parallel/inline_diff_row into utility file (Targeting %13.5)
4. Add non-HTML table layout version of diff_row behind feature flag (Targeting %13.5)
5. Remove parallel/inline_diff_row components and feature flag (Targeting %13.5)

Screenshots

n/a

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