Resolve "Improve tooltips of collapsed sidebars"

Corresponding MRs

• EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5212

What does this MR do?

Adds the following tooltips for issues/merge requests:

• Expand/collapse button
• Todo
• Assignee
• Milestone
• Time tracking
• No due date
• Labels
• Confidentiality
• Lock issue
• Participants
• Notifications
• Reference
• Move issue

Screenshots/Videos

See videos of the tooltips in action in the EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5212#screenshotsvideos

Are there points in the code the reviewer needs to double check?

Confirm if tests are needed for these tooltips.

Why was this MR needed?

Requested by #25010 (closed).

Does this MR meet the acceptance criteria?

• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #25010 (closed) Closes #44272 (closed)