Add frontend details to Merge Requests diffs technical documentation

Context

This is a follow up of a previously scheduled issue.

• Previous issue: #381604 (closed)
• MR: !106087 (merged)
• File: doc/development/merge_request_diffs.md

Goal

Add details of the frontend parts we use to render diffs in the context of Performance.

This is to assist in identifying targets for refactoring and improvements.

See previous issue for more context.