fix(ui-shell): set aria-current when current class styling added

[warrenmblood]

Closes #16885

Sets aria-current="true" when current class styling is added to a header menu item. A screen reader will now indicate the menu item that has different styling.

Changelog

New

• moved existing calculation for adding current class into a boolean variable. If true, it will also set aria-current="true" when rendering the menu item.

Changed

• updated unit test for setting current class to also check aria-current="true"
• updated docs for isActive prop to note this effect

Testing / Reviewing

• Checked in storybook that aria-current=true for menu item with current class "cds--header__menu-item--current" added
• Verified screen reader (VoiceOver) in Firefox and Chrome announces item with current styling
• Updated unit test passes

PR Checklist

As the author of this PR, before marking ready for review, confirm you:

• Reviewed every line of the diff
• Updated documentation and storybook examples
• Wrote passing tests that cover this change
• Addressed any impact on accessibility (a11y)
• Tested for cross-browser consistency
• Validated that this code is ready for review and status checks should pass

More details can be found in the pull request guide

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.85%. Comparing base (987bf7e) to head (dff635b).
Report is 15 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #19348   +/-   ##
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  Coverage   84.85%   84.85%           
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  Files         371      371           
  Lines       14413    14414    +1     
  Branches     4750     4751    +1     
=======================================
+ Hits        12230    12231    +1     
  Misses       2036     2036           
  Partials      147      147           

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[carbon-automation]

Hey there! v11.83.0 was just released that references this issue/PR.