Work item features - Rollout `work_item_features_field` FF
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=587972) </details> <!--IssueSummary end--> **Phase 4-6**: Rollout and cleanup of the `work_item_features_field` feature flag. Progressively enable the feature flag for internal users (GitLab team members), monitor for issues, and eventually remove the old `widgets` code paths once confident in the new implementation. This includes turning on the flag, validating stability, and cleaning up legacy code. ### Requirements 1. Make sure to progressively update each feature flag disabled in feature specs. Right now it's disabled globally in `spec/spec_helper.rb` 2. Make sure to remove the extended query text size from the specs added in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/222922/diffs?commit_id=d4f2730dd2e444f652fc0442ad9deeab6268b3b8 3. remove the QA spec stubbing of the flag in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/222922/diffs?commit_id=4d5218985732abed9d1d1a64c29ac53321ce5673 As we iterate, we can either manually enable them, or remove the stub and make sure all pass
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