fix: Highlight the first select option by default if none are selected

[avinashbot]

Description

NVDA borks if there's no aria-activedescendant on a focused listbox. So we select the first one by default.

Had to modify a bunch of tests because of the "screen reader text" internal implementation logic that leads to .textContent being duplicated. Thankfully .toHaveTextContent() seems to be immune to that, so I just switched to that instead.

Related links, issue #, if available: AWSUI-60825

How has this been tested?

Fought and defeated the unit tests.

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]

We need this because index 0 may not be focusable. So we need to walk from the beginning to find the first one, which is what moveHighlightFrom does.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.55%. Comparing base (bdfe392) to head (05a88fe).
Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #3546    +/-   ##
========================================
  Coverage   96.55%   96.55%            
========================================
  Files         804      807     +3     
  Lines       23439    23474    +35     
  Branches     7753     8188   +435     
========================================
+ Hits        22631    22666    +35     
+ Misses        801      754    -47     
- Partials        7       54    +47     

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