fix: focus sentinel text being read by jaws

[jlongshore]

Closes #16389

Visually hidden link "Focus sentinel" is announced by the screen reader before notifications title and after close button.

Changelog

Changed

• Added aria-hidden properties to visually hidden "Focus sentinel" elements.
• Noticed a few stories (ComposedModal.featureflag.stories.js and Modal.featureflag.stories.js) referring to the enable-preview-focus-wrap-without-sentinels feature flag, which I couldn't find in the codebase, so I renamed to enable-focus-wrap-without-sentinels.

Testing / Reviewing

• Ran storybook, visually inspected elements for aria-hidden, focus trapping appeared to work as before
• Updated snapshots / ran (and passed) tests
• Solution seems to follow "Passed Example 4" found on w3c
• Needs testing with assistive application like JAWS or similar (Tried with VoiceOver built into mac, but it doesn't seem to honor aria labels very well)

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 Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.61%. Comparing base (6e1243f) to head (e4106a0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #21123   +/-   ##
=======================================
  Coverage   92.60%   92.61%           
=======================================
  Files         515      515           
  Lines       38225    38225           
  Branches     5871     5813   -58     
=======================================
+ Hits        35399    35401    +2     
+ Misses       2676     2675    -1     
+ Partials      150      149    -1     

Flag	Coverage Δ
main-packages	85.61% <ø> (ø)
web-components	96.89% <ø> (+<0.01%)	⬆️

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[tay1orjones]

IIRC in the past aria-hidden wasn't put on the sentinel nodes because they're technically still focusable and shouldn't be removed from the accessibility tree. There might be some past issue/discussions on the topic.

[jlongshore]

IIRC in the past aria-hidden wasn't put on the sentinel nodes because they're technically still focusable and shouldn't be removed from the accessibility tree. There might be some past issue/discussions on the topic.

Ahh... yeah I'm missing any of that past discussion... and with the ability to use feature flags to get around the sentinel issue, should we just close this @tay1orjones?

[alisonjoseph]

@jlongshore @tay1orjones I think we still want the updated feature flag naming you have here regardless even if we revert the aria-hidden change?