As described in https://github.com/Automattic/themes/issues/3520,
certain child themes of Varia and Seedlet were not handling menu links
correctly when they were navigating to anchor IDs on the page the user
was currently on. An existing bit of logic was already implemented in
the twentytwentyone theme to address this use case, so this diff ports
it into the asset scripts for Varia and Seedlet as well.
Ported from D62296-code
* Scope focus styles to the site.
* Implement keyboard navigation trapping in menu modal.
* Change taborder of menu buttons.
* Cleanup focus selector.
* Fix keyboard nav within modal.
* Refactor primary menu logic to enable correct tab order.
* Refactor to work with multiple navs.
* Fix empty cart bug.
* Fix package name, missed escapes, and variable prefixing.
* Remove accidental commit of experimental link color commenting out.
* Remove a line to trigger a diff.
* Remove second translation function.
* Rename menu variable.
* Update theme URI.
* Prefix global message variable.
