Migrate MR rapid diffs page to Vue 3

Thomas Randolphrequested to merge
tor/vue3/mr-rapid-diffs into master

What does this MR do and why?

Migrates the projects.merge_requests.rapid_diffs page entrypoint to Vue 3 via @vue/compat, behind a feature flag, using the standard vue3_migration.yml flow.

Adds two files: a beta feature flag vue3_migrate_mr_rapid_diffs and a vue3_migration.yml (status: rollout) next to the entrypoint's index.js. No application logic changes.

The page is CE-only and mounts a single app, so Option 1 (page-entrypoint flag) is appropriate.

How to set up and validate locally

  1. Restart vite: gdk restart vite.
  2. Enable the feature flag vue3_migrate_mr_rapid_diffs.
  3. Load a merge request's rapid diffs page.
  4. Confirm the console logs the Vue 3 marker: [gitlab] [V] Using Vue.js 3 (with @vue/compat).
  5. Confirm document.querySelectorAll('[data-gitlab-vue3-app]') returns the app.
  6. Smoke test diff viewing and file navigation.

Related

Part of the Vue 3 migration (Code Review) epic, work item gitlab-org#23167.

Closes #611465.

Edited by Thomas Randolph

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