chore: Change all remaining internal uses of aria-live to LiveRegion component

[avinashbot]

Description

Also added a new internal LiveRegion API, preventInitialAnnouncement. May externalize it if it proves helpful, but for now, it's internal-only and opt-in.

Related links, issue #, if available: AWSUI-22299

How has this been tested?

Kept existing tests, which should continue working. Manually tested the two cases on VoiceOver.

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[avinashbot]

After a bit of manual testing, I'm honestly not sure why this was wrapped with an aria-live — there's nothing dynamically changing in the tutorial list. I believe the purpose this was supposed to serve was essentially replaced by the newly added focus-on-complete behavior in #4167.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.40%. Comparing base (a4aa195) to head (039a1d6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4470   +/-   ##
=======================================
  Coverage   97.40%   97.40%           
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  Files         933      933           
  Lines       29486    29493    +7     
  Branches    10697    10699    +2     
=======================================
+ Hits        28720    28727    +7     
  Misses        759      759           
  Partials        7        7           

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