Add controls for excluding truncation, hiding sidebar in work items

What does this MR do and why?

Adds a "View options" menu with user-scoped controls for truncation and sidebar visibility. Both settings persist across work items currently only as local storage.

Follow up: If this direction moves forward, will add a keyboard shortcut for toggling sidebar, tentatively cmd+/

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• https://gitlab.com/gitlab-org/gitlab/-/issues/512715
• Closes #524843 (closed)

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

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

md+
xs-sm or lg+drawer (sidebar reflows to body)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Open a work item such as an epic or task
2. Use the actions menu to toggle controls
   1. To test description truncation, create 2 issues with long descriptions where you see "Read more" (will need to refresh if just edited as we don't truncate after editing), then disable the setting and verify both show in full
3. Resize the browser so the sidebar reflows below the description and verify it's shown and no sidebar controls are present

Related: #519553 (closed)