Admin bar: Add tooltip for new Reader placement

[allilevine]

Proposed Changes

• Similar to https://github.com/Automattic/wp-calypso/pull/92915 we're adding a tooltip to let users know about the new Reader placement in the admin bar (on the right).
• The tooltip will show until dismissed.

Why are these changes being made?

• See p1724781177782059/1724680659.727449-slack-C07GQ1Q0L6B

Testing Instructions

• Open /sites or My Home.
• Verify that you see the tooltip until it's dismissed.
• Check that when loading from a mobile or big screen, the tooltip has the correct placement.

Note I'm occasionally seeing the tooltip loading from the Help Center icon placement. We would defer it until after the Help Center icon loads, if that's replicable.

Pre-merge Checklist

• [ ] Has the general commit checklist been followed? (PCYsg-hS-p2)
• [ ] Have you written new tests for your changes?
• [ ] Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• [ ] Have you checked for TypeScript, React or other console errors?
• [ ] Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• [ ] Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• [ ] For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?