Defaults the diffs changes tab to fluid width

What does this MR do and why?

Changes the diff tab content to always use our fluid width layout, even if the user has the limited option selected. This will change not only the diff content but always the tabs, title and the breadcrumbs on the page.

Screenshots or screen recordings

How to set up and validate locally

• Enable the feature flag mr_changes_fluid_layout

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.

Closes #340761 (closed)