chore: Fixes funnel integ tests with React 18 strict mode

[pan-kot]

Description

Without these changes a number of integration tests fail when run with React 18 strict mode, reproducible here: #3829

How has this been tested?

• I tested that by running the changes with React 16 and 18, here: chore: Multi-react version tests setup #3829
• screenshot tests
• dry-run to live

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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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.14%. Comparing base (ce7b93a) to head (c365cde).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3852      +/-   ##
==========================================
- Coverage   97.14%   97.14%   -0.01%     
==========================================
  Files         844      844              
  Lines       24515    24520       +5     
  Branches     8645     8647       +2     
==========================================
+ Hits        23815    23819       +4     
- Misses        693      694       +1     
  Partials        7        7              

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[pan-kot]

The funnel is started with a 1ms timeout in the code above. If the useEffect is called in a quick succession, which is the case in React 18 strict mode, the first cleanup runs before the setTimeout callback. In that case we issue the "cancelled" event, even though the funnel was not actually started. The updated code prevents just that.

[pan-kot]

The funnel complete event is fired when the focus leaves the elements of the funnel. In case the funnel includes a modal, and that modal is opened and then dismissed - the focus is expected to come back to the trigger button, so it stays within the funnel. In React 18 strict mode, the focus does not return to the trigger (and goes to the body), causing the complete event and also worsening the UX and a11y of the modals.

This happens because the code in this useEffect also fires after the modal is opened and the dismiss button is auto-focused. As result, the document.activeElement points not to the trigger, but to the dismiss button instead, which is unexpected. We prevent that by ensuring the active element is outside of the focus-locked container.