Draft: Clarify origin of changes in merge conflicts

What does this MR do and why?

Clarify origin of changes in merge conflicts. Also:

• Applies “Title case” to the merge conflicts page title in the breadcrumb.
• Fixes button width and padding

Related to #329842

Todo

• Update https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/diffs/components/diff_row.vue#L211
• Update docs
• Try to make buttons Pajamas compliant

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. If using the GDK with seeded data, visit /gitlab-org/gitlab-test/-/merge_requests/9/diffs
2. If using an empty instance:
   1. Make changes in a new branch and create an MR
   2. Edit the same lines in the target branch
   3. Visit the MR and select “Resolve conflicts” to view the conflict editor