Admin bar: move the Reader admin bar item to the secondary group (#38…

…976)

* Move reader icon to the secondary admin bar group.

* changelog

* Add mobile styling.

* Fix menu item order on Simple.

* Fix the gap between Reader and Help Center.

* Rebase.

* Remove versioning.

* Pixel perfect

* Move padding to inner span.

* Pixel perfect

* Add code comments around the menu priorities.

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Co-authored-by: Ashar Fuadi <ashar.fuadi@automattic.com>

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/10527308850

Upstream-Ref: Automattic/jetpack@1a961a8