chore: Multi-react version tests setup

[pan-kot]

Description

The PR implements multi-react version setup for the repository, for now supporting versions 16 and 18. It is possible to run either version in the dev mode, the dev pages are deployed for both, and the integ- and motion tests are run for both versions.

The unit tests are only run on v16 for now, as it requires a significant extra effort to make them supported. The a11y tests are only run on v16 for frugality reasons: it is possible to run them on both versions, too, if considered important.

Depends on: cloudscape-design/actions#95, #3832, #3835, #3842, #3851, #3852

In order to release the changes - we need to merge the actions PR first, and then re-deploy rulesets to apply the changes to the required action names ("dry-run / Components motion tests" -> "dry-run / Components motion tests (React 16)" + "dry-run / Components motion tests (React 18)", and the same for integ tests).

How has this been tested?

I did a test run using the react-var actions brach, and with a reverted fix to the table (#3811). Expectedly, all table integ tests for tables without keyboard navigation failed: https://github.com/cloudscape-design/components/actions/runs/17406617638/job/49412605937?pr=3829

Clarification: the tests are running in the dev mode, and the strict mode is active.

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 97.19%. Comparing base (2a71e86) to head (ac0cb16).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3829   +/-   ##
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  Coverage   97.19%   97.19%           
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  Files         844      844           
  Lines       24559    24559           
  Branches     8659     8659           
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  Hits        23869    23869           
  Misses        683      683           
  Partials        7        7           

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